Merge branches 'dev' and 'dev' of https://gitea.kuijper.es/jkuijperm/expenses_manager into dev

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

expenses_manager/expenses/forms.py

@@ -1,5 +1,27 @@
 from django import forms
-from .models import Expense, Category, Income, Tag, Account, FuelEntry, Goal
+from .models import (
+    Expense,
+    Category,
+    Income,
+    Tag,
+    Account,
+    FuelEntry,
+    Goal,
+    Transfer,
+)
+
+
+def _hide_is_transfer_when_editing(form):
+    """Quita la casilla de traspaso al editar un movimiento que ya existe.
+
+    Al crear, la casilla es un atajo: lleva al formulario de traspaso, que es
+    quien crea las dos patas. Al editar no significa nada, porque convertir un
+    gasto suelto en traspaso no es editarlo (habría que inventarse la otra
+    cuenta), y marcarla solo dejaría el movimiento marcado pero sin pareja: justo
+    el estado a medias que Transfer viene a evitar.
+    """
+    if form.instance.pk:
+        form.fields.pop("is_transfer", None)
 
 
 class ExpenseForm(forms.ModelForm):
@@ -18,6 +40,8 @@ class ExpenseForm(forms.ModelForm):
             )
             self.fields["date"].input_formats = ["%Y-%m-%d"]
 
+        _hide_is_transfer_when_editing(self)
+
     class Meta:
         model = Expense
         fields = [
@@ -61,6 +85,37 @@ class IncomeForm(forms.ModelForm):
             owner=user,
             active=True,
         )
+        _hide_is_transfer_when_editing(self)
+
+
+class TransferForm(forms.ModelForm):
+    """Formulario del traspaso. Las patas no se editan aquí ni en ninguna parte:
+    las deriva Transfer.sync() de estos campos."""
+
+    class Meta:
+        model = Transfer
+        fields = ["date", "amount", "from_account", "to_account", "fee_amount"]
+        widgets = {"date": forms.DateInput(format="%Y-%m-%d", attrs={"type": "date"})}
+        labels = {
+            "from_account": "Cuenta de origen",
+            "to_account": "Cuenta de destino",
+            "fee_amount": "Comisión",
+        }
+        help_texts = {
+            "fee_amount": (
+                "Déjalo vacío si el traspaso no tiene comisión. La comisión sí "
+                "cuenta como gasto real en el dashboard y en los presupuestos."
+            ),
+        }
+
+    def __init__(self, *args, **kwargs):
+        user = kwargs.pop("user")
+        super().__init__(*args, **kwargs)
+
+        accounts = Account.objects.filter(owner=user, active=True)
+        self.fields["from_account"].queryset = accounts
+        self.fields["to_account"].queryset = accounts
+        self.fields["date"].input_formats = ["%Y-%m-%d"]
 
 
 class FuelEntryForm(forms.ModelForm):

expenses_manager/expenses/migrations/0014_category_is_system_transfer.py

@@ -0,0 +1,40 @@
+# Generated by Django 5.2.10 on 2026-09-18 08:37
+
+import django.db.models.deletion
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('expenses', '0013_expense_is_transfer_income_is_transfer'),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='category',
+            name='is_system',
+            field=models.BooleanField(default=False, help_text='Categoría creada por la app (traspasos, comisiones). No borrable.'),
+        ),
+        migrations.CreateModel(
+            name='Transfer',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('date', models.DateField()),
+                ('amount', models.DecimalField(decimal_places=2, max_digits=12)),
+                ('fee_amount', models.DecimalField(blank=True, decimal_places=2, max_digits=10, null=True)),
+                ('created_at', models.DateTimeField(auto_now_add=True)),
+                ('expense_leg', models.OneToOneField(null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='transfer_out', to='expenses.expense')),
+                ('fee_expense', models.OneToOneField(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='transfer_fee', to='expenses.expense')),
+                ('from_account', models.ForeignKey(on_delete=django.db.models.deletion.PROTECT, related_name='transfers_out', to='expenses.account')),
+                ('income_leg', models.OneToOneField(null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='transfer_in', to='expenses.income')),
+                ('owner', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='transfers', to=settings.AUTH_USER_MODEL)),
+                ('to_account', models.ForeignKey(on_delete=django.db.models.deletion.PROTECT, related_name='transfers_in', to='expenses.account')),
+            ],
+            options={
+                'ordering': ['-date'],
+            },
+        ),
+    ]

expenses_manager/expenses/migrations/0015_link_legacy_transfers.py

@@ -0,0 +1,72 @@
+"""Convierte en Transfer los traspasos históricos que estaban sueltos.
+
+Antes de que existiera Transfer, un traspaso eran dos movimientos marcados con
+is_transfer pero sin nada que los relacionara: un Expense en la cuenta de origen
+y un Income en la de destino. Aquí se emparejan y se les cuelga un Transfer.
+
+No se pueden emparejar con certeza: nada en la base de datos dice qué gasto va
+con qué ingreso. El criterio es mismo owner, mismo importe, misma fecha y cuentas
+distintas, y solo cuando en ese grupo hay exactamente un gasto y un ingreso. Los
+ambiguos (varios candidatos con el mismo importe y fecha) y los huérfanos (sin
+pareja) se dejan tal cual, con su is_transfer=True: siguen contando en los saldos
+y fuera de los análisis igual que antes, solo que sin Transfer que los orqueste.
+Emparejarlos a ojo sería inventarse datos del usuario.
+"""
+
+from collections import defaultdict
+
+from django.db import migrations
+
+
+def link_legacy_transfers(apps, schema_editor):
+    Expense = apps.get_model("expenses", "Expense")
+    Income = apps.get_model("expenses", "Income")
+    Transfer = apps.get_model("expenses", "Transfer")
+
+    # Solo las patas que aún no pertenecen a ningún Transfer.
+    expenses_by_key = defaultdict(list)
+    for expense in Expense.objects.filter(
+        is_transfer=True, transfer_out__isnull=True, transfer_fee__isnull=True
+    ):
+        expenses_by_key[(expense.owner_id, expense.amount, expense.date)].append(
+            expense
+        )
+
+    incomes_by_key = defaultdict(list)
+    for income in Income.objects.filter(is_transfer=True, transfer_in__isnull=True):
+        incomes_by_key[(income.owner_id, income.amount, income.date)].append(income)
+
+    for key, expenses in expenses_by_key.items():
+        incomes = incomes_by_key.get(key, [])
+
+        # Uno y solo uno de cada lado: cualquier otra cosa es ambigua.
+        if len(expenses) != 1 or len(incomes) != 1:
+            continue
+
+        expense, income = expenses[0], incomes[0]
+
+        if expense.account_id == income.account_id:
+            continue
+
+        Transfer.objects.create(
+            owner_id=expense.owner_id,
+            date=expense.date,
+            amount=expense.amount,
+            from_account_id=expense.account_id,
+            to_account_id=income.account_id,
+            expense_leg=expense,
+            income_leg=income,
+        )
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("expenses", "0014_category_is_system_transfer"),
+    ]
+
+    operations = [
+        # Sin marcha atrás: deshacer esto es deshacer 0014, que se lleva la tabla
+        # Transfer entera y deja las patas intactas, que es el estado de partida.
+        migrations.RunPython(link_legacy_transfers, migrations.RunPython.noop),
+    ]

expenses_manager/expenses/migrations/0016_alter_transfer_expense_leg_alter_transfer_income_leg.py

@@ -0,0 +1,24 @@
+# Generated by Django 5.2.10 on 2026-09-21 13:35
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('expenses', '0015_link_legacy_transfers'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='transfer',
+            name='expense_leg',
+            field=models.OneToOneField(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='transfer_out', to='expenses.expense'),
+        ),
+        migrations.AlterField(
+            model_name='transfer',
+            name='income_leg',
+            field=models.OneToOneField(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='transfer_in', to='expenses.income'),
+        ),
+    ]

expenses_manager/expenses/models.py

@@ -1,6 +1,7 @@
 from datetime import date
 from decimal import Decimal
-from django.db import models
+from django.core.exceptions import ObjectDoesNotExist, ValidationError
+from django.db import models, transaction
 from django.conf import settings
 from django.db.models import Sum
 from functools import cached_property
@@ -26,6 +27,11 @@ class Category(models.Model):
         related_name="children",
     )
 
+    is_system = models.BooleanField(
+        default=False,
+        help_text="Categoría creada por la app (traspasos, comisiones). No borrable.",
+    )
+
     class Meta:
         unique_together = ("name", "parent", "owner", "slug")
         verbose_name_plural = "categories"
@@ -246,6 +252,22 @@ class Expense(models.Model):
     def __str__(self):
         return "{} - {}".format(self.date, self.amount)
 
+    @property
+    def transfer(self):
+        """El Transfer del que este gasto es una pata, o None si es normal.
+
+        Cubre las dos patas de gasto de un traspaso: la de salida
+        (transfer_out) y la comisión (transfer_fee). Un gasto que pertenece a un
+        traspaso no se edita ni se borra por separado: se hace desde el
+        traspaso, que es quien mantiene las tres patas cuadradas.
+        """
+        for relation in ("transfer_out", "transfer_fee"):
+            try:
+                return getattr(self, relation)
+            except ObjectDoesNotExist:
+                continue
+        return None
+
 
 class Income(models.Model):
     owner = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
@@ -275,6 +297,220 @@ class Income(models.Model):
     def __str__(self):
         return f"{self.name} - {self.amount}"
 
+    @property
+    def transfer(self):
+        """El Transfer del que este ingreso es la pata de entrada, o None."""
+        try:
+            return self.transfer_in
+        except ObjectDoesNotExist:
+            return None
+
+
+def _system_category(user, slug, name):
+    """Categoría de sistema del usuario (traspasos, comisiones), creándola si falta.
+
+    Se busca por slug y no por nombre porque el nombre lo puede cambiar el
+    usuario; el slug es el identificador estable.
+    """
+    cat, _ = Category.objects.get_or_create(
+        slug=slug,
+        owner=user,
+        defaults={"name": name, "is_system": True},
+    )
+    return cat
+
+
+class Transfer(models.Model):
+    """Un traspaso entre dos cuentas propias.
+
+    No sustituye a los dos movimientos que ya registraban un traspaso: los
+    orquesta. Sigue habiendo un Expense en la cuenta origen y un Income en la
+    destino, los dos con is_transfer=True, pero ahora están vinculados aquí y
+    es este modelo quien los crea, los edita y los borra a la vez (sync() y
+    delete()).
+
+    Por eso los cuatro métodos de saldo de Account (current_balance,
+    monthly_balance, balance_until, monthly_net) no saben nada de Transfer y no
+    necesitan saberlo: el traspaso ya está dentro de sus sumas, porque sus dos
+    patas siguen siendo un Income y un Expense reales.
+    """
+
+    TRANSFER_CATEGORY_SLUG = "traspaso"
+    FEE_CATEGORY_SLUG = "comision"
+
+    owner = models.ForeignKey(
+        settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name="transfers"
+    )
+    date = models.DateField()
+    # max_digits=12 frente a los 10 de Expense.amount: un traspaso de más de diez
+    # dígitos no cabría en su pata de gasto. Se deja así a propósito, porque
+    # igualarlo obliga a migrar Expense por un caso de 100 millones de euros.
+    amount = models.DecimalField(max_digits=12, decimal_places=2)
+    from_account = models.ForeignKey(
+        Account, on_delete=models.PROTECT, related_name="transfers_out"
+    )
+    to_account = models.ForeignKey(
+        Account, on_delete=models.PROTECT, related_name="transfers_in"
+    )
+
+    # Las dos patas y la comisión opcional. SET_NULL para que si algo las borra
+    # por fuera el Transfer no arrastre, pero el flujo normal las borra en cascada
+    # desde el propio Transfer (ver delete()).
+    #
+    # blank=True porque un traspaso siempre acaba con sus dos patas, pero no las
+    # tiene en el instante en que se construye: sync() las crea a partir de él.
+    # Exigirlas en full_clean() describiría mal ese momento.
+    expense_leg = models.OneToOneField(
+        Expense,
+        on_delete=models.SET_NULL,
+        null=True,
+        blank=True,
+        related_name="transfer_out",
+    )
+    income_leg = models.OneToOneField(
+        Income,
+        on_delete=models.SET_NULL,
+        null=True,
+        blank=True,
+        related_name="transfer_in",
+    )
+
+    fee_amount = models.DecimalField(
+        max_digits=10, decimal_places=2, null=True, blank=True
+    )
+    fee_expense = models.OneToOneField(
+        Expense,
+        on_delete=models.SET_NULL,
+        null=True,
+        blank=True,
+        related_name="transfer_fee",
+    )
+
+    created_at = models.DateTimeField(auto_now_add=True)
+
+    class Meta:
+        ordering = ["-date"]
+
+    def __str__(self):
+        return f"{self.date} - {self.amount} ({self.from_account} → {self.to_account})"
+
+    def clean(self):
+        if self.from_account_id and self.from_account_id == self.to_account_id:
+            raise ValidationError(
+                {"to_account": "El origen y el destino tienen que ser cuentas distintas."}
+            )
+
+    @transaction.atomic
+    def sync(self):
+        """Guarda el traspaso y pone sus patas al día en la misma transacción.
+
+        Un solo método para crear y para editar: si no hay patas las crea, y si
+        las hay les propaga importe, fecha y cuentas (la categoría no, que el
+        usuario puede haberla recolocado). La comisión aparece o desaparece
+        según fee_amount.
+
+        Ojo con la comisión: va con is_transfer=False a propósito. Las dos patas
+        del movimiento solo mueven dinero entre cuentas propias y no son gasto
+        real, pero la comisión sale del patrimonio de verdad, así que es un gasto
+        normal y tiene que contar en el dashboard y en los presupuestos.
+        """
+        if self.expense_leg_id:
+            leg = self.expense_leg
+            leg.date = self.date
+            leg.amount = self.amount
+            leg.account = self.from_account
+            leg.description = self._expense_description()
+            leg.save()
+        else:
+            self.expense_leg = Expense.objects.create(
+                owner=self.owner,
+                account=self.from_account,
+                category=_system_category(
+                    self.owner, self.TRANSFER_CATEGORY_SLUG, "Traspaso"
+                ),
+                amount=self.amount,
+                date=self.date,
+                description=self._expense_description(),
+                is_transfer=True,
+            )
+
+        if self.income_leg_id:
+            leg = self.income_leg
+            leg.date = self.date
+            leg.amount = self.amount
+            leg.account = self.to_account
+            leg.name = self._income_name()
+            leg.save()
+        else:
+            self.income_leg = Income.objects.create(
+                owner=self.owner,
+                account=self.to_account,
+                name=self._income_name(),
+                amount=self.amount,
+                date=self.date,
+                is_transfer=True,
+            )
+
+        # La comisión que sobra se borra después de guardar el Transfer, para no
+        # dejar ni un instante el FK apuntando a una fila que ya no existe.
+        stale_fee = None
+
+        if self.fee_amount:
+            if self.fee_expense_id:
+                fee = self.fee_expense
+                fee.date = self.date
+                fee.amount = self.fee_amount
+                fee.account = self.from_account
+                fee.save()
+            else:
+                self.fee_expense = Expense.objects.create(
+                    owner=self.owner,
+                    account=self.from_account,
+                    category=_system_category(
+                        self.owner, self.FEE_CATEGORY_SLUG, "Comisión"
+                    ),
+                    amount=self.fee_amount,
+                    date=self.date,
+                    description=self._fee_description(),
+                    is_transfer=False,
+                )
+        elif self.fee_expense_id:
+            stale_fee = self.fee_expense
+            self.fee_expense = None
+
+        self.save()
+
+        if stale_fee is not None:
+            stale_fee.delete()
+
+        return self
+
+    @transaction.atomic
+    def delete(self, *args, **kwargs):
+        """Borra el traspaso y sus tres patas.
+
+        Las patas son SET_NULL, así que borrarlas no arrastraría el Transfer;
+        el arrastre va en este sentido, y va aquí y no en la vista para que
+        valga también desde el shell o los tests.
+        """
+        legs = [self.expense_leg, self.income_leg, self.fee_expense]
+        result = super().delete(*args, **kwargs)
+
+        for leg in legs:
+            if leg is not None:
+                leg.delete()
+
+        return result
+
+    def _expense_description(self):
+        return f"Traspaso a {self.to_account.name}"
+
+    def _income_name(self):
+        return f"Traspaso desde {self.from_account.name}"
+
+    def _fee_description(self):
+        return f"Comisión del traspaso a {self.to_account.name}"
+
 
 class FuelEntry(models.Model):
     expense = models.OneToOneField(

expenses_manager/expenses/static/expenses/js/transfer_redirect.js

@@ -0,0 +1,51 @@
+// Al marcar la casilla de traspaso en el formulario de gasto o de ingreso, salta
+// al formulario de traspaso llevándose fecha, importe y cuenta. El movimiento no
+// se guarda: un traspaso son dos patas y las crea Transfer.sync().
+//
+// Esto es solo un atajo para no obligar a enviar el formulario: si el JS no corre,
+// la vista hace la misma redirección al recibir el POST, así que el
+// comportamiento no depende de este fichero.
+document.addEventListener('DOMContentLoaded', function () {
+    var form = document.querySelector('[data-transfer-url]');
+
+    if (!form) {
+        return;
+    }
+
+    var checkbox = form.querySelector('#id_is_transfer');
+
+    if (!checkbox) {
+        return;  // editando no se pinta la casilla
+    }
+
+    // Qué cuenta es la del formulario en el traspaso: origen si es un gasto,
+    // destino si es un ingreso. Lo decide la plantilla, no este fichero.
+    var accountParam = form.dataset.transferAccountParam;
+
+    checkbox.addEventListener('change', function () {
+        if (!checkbox.checked) {
+            return;
+        }
+
+        var params = new URLSearchParams();
+
+        ['date', 'amount'].forEach(function (name) {
+            var field = form.querySelector('[name="' + name + '"]');
+
+            if (field && field.value) {
+                params.set(name, field.value);
+            }
+        });
+
+        var account = form.querySelector('[name="account"]');
+
+        if (account && account.value) {
+            params.set(accountParam, account.value);
+        }
+
+        var query = params.toString();
+        window.location.href = query
+            ? form.dataset.transferUrl + '?' + query
+            : form.dataset.transferUrl;
+    });
+});

expenses_manager/expenses/templates/categories/confirm_delete.html

@@ -7,7 +7,12 @@
 {% block delete_question %}¿Seguro que quieres eliminar la categoría <strong>{{ category.name }}</strong>?{% endblock %}
 
 {% block delete_warnings %}
-    {% if expense_count %}
+    {% if category.is_system %}
+        <p class="form-errors">
+            Esta categoría la usa la aplicación para clasificar los traspasos y sus
+            comisiones, así que no se puede eliminar.
+        </p>
+    {% elif expense_count %}
         <p class="form-errors">
             Esta categoría tiene {{ expense_count }} gasto{{ expense_count|pluralize }} asociado{{ expense_count|pluralize }}
             y no se puede eliminar. Reasigna esos gastos a otra categoría primero.

expenses_manager/expenses/templates/categories/list.html

@@ -30,11 +30,18 @@
             <tbody>
                 {% for row in category_rows %}
                 <tr>
-                    <td class="cat-depth-{{ row.depth }}">{{ row.category.name }}</td>
+                    <td class="cat-depth-{{ row.depth }}">
+                        {{ row.category.name }}
+                        {% if row.category.is_system %}
+                            <span class="badge badge-neutral">Del sistema</span>
+                        {% endif %}
+                    </td>
                     <td>{{ row.category.expense_count }}</td>
                     <td class="table-actions">
                         <a href="{% url 'category_edit' row.category.id %}">Editar</a>
+                        {% if not row.category.is_system %}
                             <a href="{% url 'category_delete' row.category.id %}" class="danger">Eliminar</a>
+                        {% endif %}
                     </td>
                 </tr>
                 {% empty %}

expenses_manager/expenses/templates/expenses/base.html

@@ -33,6 +33,7 @@
                     <a href="{% url 'dashboard' %}" class="nav-item {% if active_menu == 'dashboard' %}active{% endif %} ">Dashboard</a>
                     <a href="{% url 'expense_list' %}" class="nav-item {% if active_menu == 'expenses' %}active{% endif %} ">Gastos</a>
                     <a href="{% url 'income_list' %}" class="nav-item {% if active_menu == 'incomes' %}active{% endif %} ">Ingresos</a>
+                    <a href="{% url 'transfer_list' %}" class="nav-item {% if active_menu == 'transfers' %}active{% endif %} ">Traspasos</a>
                     <a href="{% url 'fuel_list' %}" class="nav-item {% if active_menu == 'fuel' %}active{% endif %} ">Repostajes</a>
                     <a href="{% url 'account_list' %}" class="nav-item {% if active_menu == 'accounts' %}active{% endif %} ">Cuentas</a>
                     <div class="nav-item dropdown {% if active_menu == 'settings' %}active{% endif %}" id="settingsDropdown">

expenses_manager/expenses/templates/expenses/expense_form.html

@@ -1,4 +1,5 @@
 {% extends "expenses/base.html" %}
+{% load static %}
 
 {% block title %}
     {% if form.instance.pk %}
@@ -17,7 +18,9 @@
         {% endif %}
     </h1>
 
-    <form method="post" class="app-form">
+    <form method="post" class="app-form"
+          data-transfer-url="{% url 'transfer_create' %}"
+          data-transfer-account-param="from_account">
         {% csrf_token %}
 
         {% include "expenses/_form_fields.html" %}
@@ -34,3 +37,7 @@
         </div>
     </form>
 {% endblock %}
+
+{% block extra_js %}
+    <script src="{% static 'expenses/js/transfer_redirect.js' %}" defer></script>
+{% endblock %}

expenses_manager/expenses/templates/expenses/expense_list.html

@@ -145,7 +145,10 @@
                         {% endfor %}
                     </td>
                     <td class="table-actions">
-                        {% if expense.fuel_data %}
+                        {% if expense.transfer %}
+                            {# Pata de un traspaso: se edita y se borra desde el traspaso. #}
+                            <a href="{% url 'transfer_edit' expense.transfer.id %}">Editar traspaso</a>
+                        {% elif expense.fuel_data %}
                             <a href="{% url 'fuel_edit' expense.id %}?next={{ request.get_full_path|urlencode }}">Editar</a>
                             <a href="{% url 'fuel_delete' expense.id %}?next={{ request.get_full_path|urlencode }}" class="danger">Eliminar</a>
                         {% else %}

expenses_manager/expenses/templates/expenses/income_form.html

@@ -1,4 +1,5 @@
 {% extends "expenses/base.html" %}
+{% load static %}
 {% block title %}
             {% if form.instance.pk %}
                 Editar ingreso
@@ -16,7 +17,9 @@
         {% endif %}
     </h1>
 
-    <form method="post" class="app-form">
+    <form method="post" class="app-form"
+          data-transfer-url="{% url 'transfer_create' %}"
+          data-transfer-account-param="to_account">
         {% csrf_token %}
         {% include "expenses/_form_fields.html" %}
         <div class="form-actions">
@@ -31,3 +34,7 @@
         </div>
     </form>
 {% endblock %}
+
+{% block extra_js %}
+    <script src="{% static 'expenses/js/transfer_redirect.js' %}" defer></script>
+{% endblock %}

expenses_manager/expenses/templates/expenses/income_list.html

@@ -93,8 +93,13 @@
                     <td>{{ income.amount|floatformat:2 }}</td>
                     <td>{{ income.date }}</td>
                     <td class="table-actions">
+                        {% if income.transfer %}
+                            {# Pata de un traspaso: se edita y se borra desde el traspaso. #}
+                            <a href="{% url 'transfer_edit' income.transfer.id %}">Editar traspaso</a>
+                        {% else %}
                             <a href="{% url 'income_edit' income.id %}">Editar</a>
                             <a href="{% url 'income_delete' income.id %}" class="danger">Eliminar</a>
+                        {% endif %}
                     </td>
                 </tr>
             {% empty %}

expenses_manager/expenses/templates/transfers/confirm_delete.html

@@ -0,0 +1,23 @@
+{% extends "expenses/_confirm_delete.html" %}
+
+{% block title %}Traspasos{% endblock %}
+
+{% block delete_heading %}Eliminar traspaso{% endblock %}
+
+{% block delete_question %}
+    ¿Seguro que quieres eliminar el traspaso de
+    <strong>{{ transfer.amount|floatformat:2 }}€</strong>
+    de <strong>{{ transfer.from_account.name }}</strong>
+    a <strong>{{ transfer.to_account.name }}</strong>
+    del {{ transfer.date }}?
+{% endblock %}
+
+{% block delete_warnings %}
+    <p class="form-errors">
+        Se eliminarán también el gasto de la cuenta de origen y el ingreso de la de
+        destino{% if transfer.fee_amount %}, además del gasto de la comisión{% endif %}.
+        Los saldos de las dos cuentas volverán a como estaban.
+    </p>
+{% endblock %}
+
+{% block cancel_url %}{% url 'transfer_list' %}{% endblock %}

expenses_manager/expenses/templates/transfers/form.html

@@ -0,0 +1,29 @@
+{% extends "expenses/base.html" %}
+
+{% block title %}{{ title }}{% endblock %}
+
+{% block content %}
+    <h1>{{ title }}</h1>
+
+    {% if form.instance.pk %}
+        <p>
+            Al guardar se actualizan los dos movimientos del traspaso y su comisión.
+            No hace falta tocarlos por separado en Gastos ni en Ingresos.
+        </p>
+    {% endif %}
+
+    <form method="post" class="app-form">
+        {% csrf_token %}
+        {% include "expenses/_form_fields.html" %}
+        <div class="form-actions">
+            <button type="submit" class="btn btn-primary">
+                {% if form.instance.pk %}
+                    Guardar traspaso
+                {% else %}
+                    Crear traspaso
+                {% endif %}
+            </button>
+            <a class="btn btn-secondary" href="{% url 'transfer_list' %}">Volver</a>
+        </div>
+    </form>
+{% endblock %}

expenses_manager/expenses/templates/transfers/list.html

@@ -0,0 +1,64 @@
+{% extends "expenses/base.html" %}
+
+{% block title %}
+    Traspasos
+{% endblock %}
+
+{% block content %}
+    <h1>Mis traspasos</h1>
+
+    <p>
+        Un traspaso mueve dinero entre dos cuentas propias: no cuenta como gasto ni
+        como ingreso en los análisis, pero sí cambia el saldo de las dos cuentas.
+        La comisión, si la hay, sí es un gasto real.
+    </p>
+
+    <div class="section-actions">
+        <a class="btn btn-primary" href="{% url 'transfer_create' %}">➕ Nuevo traspaso</a>
+    </div>
+
+    <br>
+
+    <div class="table-wrap">
+        <table>
+            <thead>
+                <tr>
+                    <th>Fecha</th>
+                    <th>Origen</th>
+                    <th>Destino</th>
+                    <th>Importe</th>
+                    <th>Comisión</th>
+                    <th></th>
+                </tr>
+            </thead>
+            <tbody>
+                {% for transfer in transfers %}
+                    <tr>
+                        <td>{{ transfer.date }}</td>
+                        <td>{{ transfer.from_account.name }}</td>
+                        <td>{{ transfer.to_account.name }}</td>
+                        <td>{{ transfer.amount|floatformat:2 }}€</td>
+                        <td>
+                            {% if transfer.fee_amount %}
+                                {{ transfer.fee_amount|floatformat:2 }}€
+                            {% else %}
+                                <span>-</span>
+                            {% endif %}
+                        </td>
+                        <td class="table-actions">
+                            <a href="{% url 'transfer_edit' transfer.id %}">Editar</a>
+                            <a href="{% url 'transfer_delete' transfer.id %}" class="danger">Eliminar</a>
+                        </td>
+                    </tr>
+                {% empty %}
+                    <tr>
+                        <td colspan="6" class="empty-state">
+                            <p>No hay traspasos</p>
+                            <a href="{% url 'transfer_create' %}">Añade el primero</a>
+                        </td>
+                    </tr>
+                {% endfor %}
+            </tbody>
+        </table>
+    </div>
+{% endblock %}

expenses_manager/expenses/tests/test_categories.py

@@ -101,6 +101,26 @@ def test_category_delete_without_expenses_succeeds(auth_client, user):
     assert not Category.objects.filter(pk=cat.pk).exists()
 
 
+def test_system_category_cannot_be_deleted(auth_client, user):
+    """Las categorías de traspaso y comisión las pone la app, no el usuario."""
+    cat = Category.objects.create(name="Traspaso", owner=user, is_system=True)
+
+    response = auth_client.post(reverse('category_delete', args=[cat.pk]))
+
+    assert response.status_code == 302
+    assert Category.objects.filter(pk=cat.pk).exists()
+    messages = [str(m) for m in get_messages(response.wsgi_request)]
+    assert any("traspasos" in m for m in messages)
+
+
+def test_system_category_has_no_delete_link_in_the_list(auth_client, user):
+    cat = Category.objects.create(name="Traspaso", owner=user, is_system=True)
+
+    response = auth_client.get(reverse('category_list'))
+
+    assert reverse('category_delete', args=[cat.pk]) not in response.content.decode()
+
+
 def test_category_list_view_returns_tree_ordered_with_depth(auth_client, user):
     root_a = Category.objects.create(name="A raiz", owner=user)
     Category.objects.create(name="B raiz", owner=user)

expenses_manager/expenses/tests/test_transfer_model.py

@@ -0,0 +1,977 @@
+"""El modelo Transfer: orquesta las dos patas de un traspaso.
+
+Transfer no sustituye al Expense de salida y al Income de entrada: los crea, los
+vincula y los mantiene sincronizados. De ahí que aquí no se compruebe ningún
+método de saldo nuevo, sino que los de siempre siguen dando el número correcto
+porque las patas siguen siendo un gasto y un ingreso reales.
+
+El punto más delicado, y el que más tests tiene: la comisión va con
+is_transfer=False, porque es dinero que sale del patrimonio de verdad y sí tiene
+que contar en los análisis.
+"""
+
+import importlib
+from datetime import date
+from decimal import Decimal
+from urllib.parse import parse_qs, urlparse
+
+import pytest
+from django.apps import apps as django_apps
+from django.core.exceptions import ValidationError
+from django.urls import reverse
+
+from expenses.models import Account, Category, Expense, Income, Transfer
+
+pytestmark = pytest.mark.django_db
+
+
+@pytest.fixture
+def savings(user):
+    return Account.objects.create(
+        owner=user, name="Ahorro", initial_balance=Decimal("0"), active=True
+    )
+
+
+def make_transfer(user, from_account, to_account, amount="400", on=None, fee=None):
+    transfer = Transfer(
+        owner=user,
+        date=on or date(2024, 5, 11),
+        amount=Decimal(amount),
+        from_account=from_account,
+        to_account=to_account,
+        fee_amount=Decimal(fee) if fee is not None else None,
+    )
+    transfer.sync()
+    return transfer
+
+
+# --------------------------------------------------------------------------
+# Creación: las dos patas
+# --------------------------------------------------------------------------
+
+
+def test_creating_a_transfer_builds_and_links_both_legs(user, account, savings):
+    transfer = make_transfer(user, account, savings)
+
+    assert transfer.expense_leg is not None
+    assert transfer.income_leg is not None
+
+    assert transfer.expense_leg.account == account
+    assert transfer.expense_leg.amount == Decimal("400")
+    assert transfer.expense_leg.date == transfer.date
+    assert transfer.expense_leg.owner == user
+    assert transfer.expense_leg.is_transfer is True
+
+    assert transfer.income_leg.account == savings
+    assert transfer.income_leg.amount == Decimal("400")
+    assert transfer.income_leg.date == transfer.date
+    assert transfer.income_leg.owner == user
+    assert transfer.income_leg.is_transfer is True
+
+    # El vínculo se ve desde las dos puntas.
+    assert transfer.expense_leg.transfer == transfer
+    assert transfer.income_leg.transfer == transfer
+
+
+def test_legs_use_the_system_transfer_category(user, account, savings):
+    transfer = make_transfer(user, account, savings)
+
+    leg_category = transfer.expense_leg.category
+    assert leg_category.slug == "traspaso"
+    assert leg_category.is_system is True
+    assert leg_category.owner == user
+
+
+def test_two_transfers_share_the_same_system_category(user, account, savings):
+    first = make_transfer(user, account, savings)
+    second = make_transfer(user, account, savings, on=date(2024, 6, 11))
+
+    assert first.expense_leg.category_id == second.expense_leg.category_id
+    assert Category.objects.filter(owner=user, slug="traspaso").count() == 1
+
+
+def test_both_balances_move(user, account, savings):
+    account.initial_balance = Decimal("1000")
+    account.save()
+
+    make_transfer(user, account, savings)
+
+    assert account.current_balance() == Decimal("600")
+    assert savings.current_balance() == Decimal("400")
+
+
+def test_transfer_does_not_change_the_total_patrimony(user, account, savings):
+    account.initial_balance = Decimal("1000")
+    account.save()
+
+    make_transfer(user, account, savings)
+
+    total = account.current_balance() + savings.current_balance()
+    assert total == Decimal("1000")
+
+
+# --------------------------------------------------------------------------
+# La comisión: un gasto real, sin is_transfer
+# --------------------------------------------------------------------------
+
+
+def test_fee_creates_a_third_expense_that_is_not_a_transfer(user, account, savings):
+    transfer = make_transfer(user, account, savings, fee="3")
+
+    assert transfer.fee_expense is not None
+    assert transfer.fee_expense.amount == Decimal("3")
+    assert transfer.fee_expense.account == account
+    assert transfer.fee_expense.date == transfer.date
+    # El punto donde es más fácil equivocarse: la comisión NO es un traspaso.
+    assert transfer.fee_expense.is_transfer is False
+    assert transfer.fee_expense.category.slug == "comision"
+    assert transfer.fee_expense.category.is_system is True
+
+
+def test_fee_is_charged_to_the_origin_account(user, account, savings):
+    account.initial_balance = Decimal("1000")
+    account.save()
+
+    make_transfer(user, account, savings, fee="3")
+
+    # El origen paga el traspaso y la comisión; el destino solo recibe el traspaso.
+    assert account.current_balance() == Decimal("597")
+    assert savings.current_balance() == Decimal("400")
+
+
+def test_dashboard_counts_the_fee_but_not_the_legs(auth_client, user, account, savings):
+    make_transfer(user, account, savings, fee="3", on=date(2024, 5, 11))
+
+    response = auth_client.get(reverse("dashboard"), {"year": 2024})
+
+    assert response.context["kpi_total"] == Decimal("3")
+    assert response.context["kpi_count"] == 1
+
+    rows = {row["category__name"]: row["total"] for row in response.context["by_category"]}
+    assert rows == {"Comisión": Decimal("3")}
+
+
+def test_without_fee_the_dashboard_sees_nothing(auth_client, user, account, savings):
+    make_transfer(user, account, savings, on=date(2024, 5, 11))
+
+    response = auth_client.get(reverse("dashboard"), {"year": 2024})
+
+    assert response.context["kpi_total"] == Decimal("0")
+    assert response.context["kpi_count"] == 0
+
+
+# --------------------------------------------------------------------------
+# Edición: sincronizar las patas
+# --------------------------------------------------------------------------
+
+
+def test_editing_the_amount_updates_both_legs(user, account, savings):
+    transfer = make_transfer(user, account, savings)
+
+    transfer.amount = Decimal("250")
+    transfer.sync()
+
+    transfer.expense_leg.refresh_from_db()
+    transfer.income_leg.refresh_from_db()
+    assert transfer.expense_leg.amount == Decimal("250")
+    assert transfer.income_leg.amount == Decimal("250")
+
+    assert account.current_balance() == Decimal("-250")
+    assert savings.current_balance() == Decimal("250")
+
+
+def test_editing_the_date_updates_both_legs(user, account, savings):
+    transfer = make_transfer(user, account, savings)
+
+    transfer.date = date(2024, 8, 1)
+    transfer.sync()
+
+    transfer.expense_leg.refresh_from_db()
+    transfer.income_leg.refresh_from_db()
+    assert transfer.expense_leg.date == date(2024, 8, 1)
+    assert transfer.income_leg.date == date(2024, 8, 1)
+
+
+def test_editing_the_accounts_moves_the_legs(user, account, savings):
+    transfer = make_transfer(user, account, savings)
+    third = Account.objects.create(
+        owner=user, name="Bolsillo", initial_balance=Decimal("0"), active=True
+    )
+
+    transfer.from_account = savings
+    transfer.to_account = third
+    transfer.sync()
+
+    transfer.expense_leg.refresh_from_db()
+    transfer.income_leg.refresh_from_db()
+    assert transfer.expense_leg.account == savings
+    assert transfer.income_leg.account == third
+    assert account.current_balance() == Decimal("0")
+
+
+def test_editing_does_not_create_new_legs(user, account, savings):
+    transfer = make_transfer(user, account, savings)
+    expense_id, income_id = transfer.expense_leg_id, transfer.income_leg_id
+
+    transfer.amount = Decimal("250")
+    transfer.sync()
+
+    assert transfer.expense_leg_id == expense_id
+    assert transfer.income_leg_id == income_id
+    assert Expense.objects.count() == 1
+    assert Income.objects.count() == 1
+
+
+def test_adding_a_fee_on_edit_creates_it(user, account, savings):
+    transfer = make_transfer(user, account, savings)
+    assert transfer.fee_expense is None
+
+    transfer.fee_amount = Decimal("3")
+    transfer.sync()
+
+    assert transfer.fee_expense is not None
+    assert transfer.fee_expense.is_transfer is False
+    assert Expense.objects.count() == 2
+
+
+def test_removing_the_fee_on_edit_deletes_it(user, account, savings):
+    transfer = make_transfer(user, account, savings, fee="3")
+    fee_id = transfer.fee_expense_id
+
+    transfer.fee_amount = None
+    transfer.sync()
+
+    assert transfer.fee_expense is None
+    assert not Expense.objects.filter(pk=fee_id).exists()
+
+    transfer.refresh_from_db()
+    assert transfer.fee_expense_id is None
+
+
+def test_editing_the_fee_amount_updates_the_expense(user, account, savings):
+    transfer = make_transfer(user, account, savings, fee="3")
+
+    transfer.fee_amount = Decimal("5")
+    transfer.sync()
+
+    transfer.fee_expense.refresh_from_db()
+    assert transfer.fee_expense.amount == Decimal("5")
+    assert Expense.objects.count() == 2
+
+
+# --------------------------------------------------------------------------
+# Borrado
+# --------------------------------------------------------------------------
+
+
+def test_deleting_the_transfer_deletes_both_legs(user, account, savings):
+    transfer = make_transfer(user, account, savings)
+
+    transfer.delete()
+
+    assert Expense.objects.count() == 0
+    assert Income.objects.count() == 0
+    assert Transfer.objects.count() == 0
+
+
+def test_deleting_the_transfer_deletes_the_fee_too(user, account, savings):
+    transfer = make_transfer(user, account, savings, fee="3")
+
+    transfer.delete()
+
+    assert Expense.objects.count() == 0
+    assert Income.objects.count() == 0
+    assert Transfer.objects.count() == 0
+
+
+def test_deleting_the_transfer_restores_both_balances(user, account, savings):
+    account.initial_balance = Decimal("1000")
+    account.save()
+    transfer = make_transfer(user, account, savings, fee="3")
+
+    transfer.delete()
+
+    assert account.current_balance() == Decimal("1000")
+    assert savings.current_balance() == Decimal("0")
+
+
+# --------------------------------------------------------------------------
+# Validación y atomicidad
+# --------------------------------------------------------------------------
+
+
+def test_same_account_on_both_sides_is_rejected(user, account):
+    transfer = Transfer(
+        owner=user,
+        date=date(2024, 5, 11),
+        amount=Decimal("400"),
+        from_account=account,
+        to_account=account,
+    )
+
+    with pytest.raises(ValidationError) as error:
+        transfer.full_clean()
+
+    assert "to_account" in error.value.message_dict
+
+
+def test_different_accounts_pass_validation(user, account, savings):
+    transfer = Transfer(
+        owner=user,
+        date=date(2024, 5, 11),
+        amount=Decimal("400"),
+        from_account=account,
+        to_account=savings,
+    )
+
+    # A pelo y sin excluir nada: las patas son blank=True porque aún no existen.
+    transfer.full_clean()  # no levanta
+
+
+def test_a_failed_leg_leaves_nothing_behind(user, account, savings, monkeypatch):
+    """Atomicidad: si la segunda pata falla, la primera no queda suelta."""
+
+    def boom(self):
+        raise RuntimeError("fallo al construir la pata de entrada")
+
+    monkeypatch.setattr(Transfer, "_income_name", boom)
+
+    transfer = Transfer(
+        owner=user,
+        date=date(2024, 5, 11),
+        amount=Decimal("400"),
+        from_account=account,
+        to_account=savings,
+    )
+
+    with pytest.raises(RuntimeError):
+        transfer.sync()
+
+    assert Expense.objects.count() == 0
+    assert Income.objects.count() == 0
+    assert Transfer.objects.count() == 0
+
+
+# --------------------------------------------------------------------------
+# Las patas no se editan por separado
+# --------------------------------------------------------------------------
+
+
+def test_expense_leg_cannot_be_edited_on_its_own(auth_client, user, account, savings):
+    transfer = make_transfer(user, account, savings)
+
+    response = auth_client.get(
+        reverse("expense_edit", args=[transfer.expense_leg_id]), follow=True
+    )
+
+    assert response.redirect_chain[0][0] == reverse("transfer_edit", args=[transfer.pk])
+
+
+def test_expense_leg_cannot_be_deleted_on_its_own(auth_client, user, account, savings):
+    transfer = make_transfer(user, account, savings)
+
+    auth_client.post(reverse("expense_delete", args=[transfer.expense_leg_id]))
+
+    assert Expense.objects.filter(pk=transfer.expense_leg_id).exists()
+
+
+def test_income_leg_cannot_be_deleted_on_its_own(auth_client, user, account, savings):
+    transfer = make_transfer(user, account, savings)
+
+    auth_client.post(reverse("income_delete", args=[transfer.income_leg_id]))
+
+    assert Income.objects.filter(pk=transfer.income_leg_id).exists()
+
+
+def test_the_fee_expense_cannot_be_edited_on_its_own(auth_client, user, account, savings):
+    transfer = make_transfer(user, account, savings, fee="3")
+
+    response = auth_client.get(
+        reverse("expense_edit", args=[transfer.fee_expense_id]), follow=True
+    )
+
+    assert response.redirect_chain[0][0] == reverse("transfer_edit", args=[transfer.pk])
+
+
+def test_a_normal_expense_is_still_editable(auth_client, user, account, category):
+    expense = Expense.objects.create(
+        owner=user,
+        account=account,
+        category=category,
+        amount=Decimal("10"),
+        date=date(2024, 5, 11),
+    )
+
+    response = auth_client.get(reverse("expense_edit", args=[expense.pk]))
+
+    assert response.status_code == 200
+    assert expense.transfer is None
+
+
+def test_the_listing_links_a_leg_to_its_transfer(auth_client, user, account, savings):
+    transfer = make_transfer(user, account, savings)
+
+    response = auth_client.get(reverse("expense_list"), {"year": 2024})
+    html = response.content.decode()
+
+    assert reverse("transfer_edit", args=[transfer.pk]) in html
+    assert reverse("expense_delete", args=[transfer.expense_leg_id]) not in html
+
+
+@pytest.mark.parametrize("listing", ["expense_list", "income_list"])
+def test_no_template_comment_leaks_into_the_listing(
+    auth_client, user, account, savings, listing
+):
+    """Los {# #} de Django son de una sola línea: partidos en dos se imprimen."""
+    make_transfer(user, account, savings)
+
+    response = auth_client.get(reverse(listing), {"year": 2024})
+
+    assert "{#" not in response.content.decode()
+
+
+# --------------------------------------------------------------------------
+# Vistas CRUD
+# --------------------------------------------------------------------------
+
+
+def test_create_view_builds_the_three_legs(auth_client, user, account, savings):
+    response = auth_client.post(
+        reverse("transfer_create"),
+        {
+            "date": "2024-05-11",
+            "amount": "400",
+            "from_account": account.id,
+            "to_account": savings.id,
+            "fee_amount": "3",
+        },
+    )
+
+    assert response.status_code == 302
+    transfer = Transfer.objects.get(owner=user)
+    assert transfer.expense_leg.is_transfer is True
+    assert transfer.income_leg.is_transfer is True
+    assert transfer.fee_expense.is_transfer is False
+
+
+def test_create_view_without_fee(auth_client, user, account, savings):
+    auth_client.post(
+        reverse("transfer_create"),
+        {
+            "date": "2024-05-11",
+            "amount": "400",
+            "from_account": account.id,
+            "to_account": savings.id,
+            "fee_amount": "",
+        },
+    )
+
+    transfer = Transfer.objects.get(owner=user)
+    assert transfer.fee_amount is None
+    assert transfer.fee_expense is None
+    assert Expense.objects.count() == 1
+
+
+def test_create_view_rejects_the_same_account_twice(auth_client, user, account):
+    response = auth_client.post(
+        reverse("transfer_create"),
+        {
+            "date": "2024-05-11",
+            "amount": "400",
+            "from_account": account.id,
+            "to_account": account.id,
+        },
+    )
+
+    assert response.status_code == 200
+    assert Transfer.objects.count() == 0
+    assert "to_account" in response.context["form"].errors
+
+
+def test_edit_view_syncs_the_legs(auth_client, user, account, savings):
+    transfer = make_transfer(user, account, savings)
+
+    response = auth_client.post(
+        reverse("transfer_edit", args=[transfer.pk]),
+        {
+            "date": "2024-05-11",
+            "amount": "250",
+            "from_account": account.id,
+            "to_account": savings.id,
+            "fee_amount": "",
+        },
+    )
+
+    assert response.status_code == 302
+    transfer.expense_leg.refresh_from_db()
+    transfer.income_leg.refresh_from_db()
+    assert transfer.expense_leg.amount == Decimal("250")
+    assert transfer.income_leg.amount == Decimal("250")
+
+
+def test_delete_view_removes_everything(auth_client, user, account, savings):
+    transfer = make_transfer(user, account, savings, fee="3")
+
+    response = auth_client.post(reverse("transfer_delete", args=[transfer.pk]))
+
+    assert response.status_code == 302
+    assert Transfer.objects.count() == 0
+    assert Expense.objects.count() == 0
+    assert Income.objects.count() == 0
+
+
+def test_delete_view_needs_post(auth_client, user, account, savings):
+    transfer = make_transfer(user, account, savings)
+
+    response = auth_client.get(reverse("transfer_delete", args=[transfer.pk]))
+
+    assert response.status_code == 200
+    assert Transfer.objects.count() == 1
+
+
+def test_list_view_only_shows_your_own(auth_client, user, account, savings, django_user_model):
+    make_transfer(user, account, savings)
+
+    other = django_user_model.objects.create_user(username="otro", password="x")
+    other_account = Account.objects.create(
+        owner=other, name="Suya", initial_balance=Decimal("0"), active=True
+    )
+    other_savings = Account.objects.create(
+        owner=other, name="Suya 2", initial_balance=Decimal("0"), active=True
+    )
+    make_transfer(other, other_account, other_savings)
+
+    response = auth_client.get(reverse("transfer_list"))
+
+    assert [t.owner for t in response.context["transfers"]] == [user]
+
+
+def test_form_only_offers_your_active_accounts(auth_client, user, account, savings):
+    Account.objects.create(
+        owner=user, name="Cerrada", initial_balance=Decimal("0"), active=False
+    )
+
+    response = auth_client.get(reverse("transfer_create"))
+    form = response.context["form"]
+
+    names = {acc.name for acc in form.fields["from_account"].queryset}
+    assert names == {account.name, savings.name}
+    assert names == {acc.name for acc in form.fields["to_account"].queryset}
+
+
+def test_transfer_edit_view_is_scoped_by_owner(auth_client, django_user_model):
+    other = django_user_model.objects.create_user(username="otro", password="x")
+    other_account = Account.objects.create(
+        owner=other, name="Suya", initial_balance=Decimal("0"), active=True
+    )
+    other_savings = Account.objects.create(
+        owner=other, name="Suya 2", initial_balance=Decimal("0"), active=True
+    )
+    transfer = make_transfer(other, other_account, other_savings)
+
+    response = auth_client.get(reverse("transfer_edit", args=[transfer.pk]))
+
+    assert response.status_code == 404
+
+
+# --------------------------------------------------------------------------
+# El atajo de la casilla: del gasto o del ingreso al traspaso
+# --------------------------------------------------------------------------
+
+
+def _query(url):
+    return parse_qs(urlparse(url).query)
+
+
+def test_the_expense_form_carries_its_data_to_the_transfer_form(
+    auth_client, user, account, category
+):
+    """La cuenta de un gasto entra como origen: el dinero sale de ahí."""
+    response = auth_client.post(
+        reverse("expense_create"),
+        {
+            "date": "2024-05-11",
+            "amount": "400",
+            "description": "",
+            "category": category.id,
+            "account": account.id,
+            "is_transfer": "on",
+        },
+    )
+
+    assert response.status_code == 302
+    assert urlparse(response.url).path == reverse("transfer_create")
+    assert _query(response.url) == {
+        "date": ["2024-05-11"],
+        "amount": ["400"],
+        "from_account": [str(account.id)],
+    }
+
+
+def test_the_income_form_carries_its_account_as_destination(auth_client, user, savings):
+    response = auth_client.post(
+        reverse("income_create"),
+        {
+            "account": savings.id,
+            "name": "Traspaso",
+            "amount": "400",
+            "date": "2024-05-11",
+            "is_transfer": "on",
+        },
+    )
+
+    assert _query(response.url) == {
+        "date": ["2024-05-11"],
+        "amount": ["400"],
+        "to_account": [str(savings.id)],
+    }
+
+
+def test_a_half_filled_expense_still_reaches_the_transfer_form(
+    auth_client, user, account
+):
+    """Sin categoría el gasto no valida, pero el salto no depende de que valide:
+    se lleva lo que haya y lo que falte se queda en blanco."""
+    response = auth_client.post(
+        reverse("expense_create"),
+        {"date": "", "amount": "400", "account": account.id, "is_transfer": "on"},
+    )
+
+    assert response.status_code == 302
+    assert _query(response.url) == {
+        "amount": ["400"],
+        "from_account": [str(account.id)],
+    }
+    assert not Expense.objects.filter(owner=user).exists()
+
+
+def test_the_transfer_form_prefills_from_the_url(auth_client, user, account, savings):
+    response = auth_client.get(
+        reverse("transfer_create"),
+        {
+            "date": "2024-05-11",
+            "amount": "400",
+            "from_account": account.id,
+            "to_account": savings.id,
+        },
+    )
+
+    assert response.context["form"].initial == {
+        "date": date(2024, 5, 11),
+        "amount": Decimal("400"),
+        "from_account": account.id,
+        "to_account": savings.id,
+    }
+
+
+@pytest.mark.parametrize(
+    "params",
+    [
+        {"date": "11/05/2024"},
+        {"date": "2024-13-45"},
+        {"amount": "cuatrocientos"},
+        {"amount": "NaN"},
+        {"amount": "Infinity"},
+        {"from_account": "primera"},
+        {"to_account": "999999"},
+    ],
+)
+def test_an_invalid_url_param_is_ignored_and_does_not_break(auth_client, user, params):
+    """La URL la escribe cualquiera: lo que no se entienda sale en blanco."""
+    response = auth_client.get(reverse("transfer_create"), params)
+
+    assert response.status_code == 200
+    assert response.context["form"].initial == {}
+
+
+def test_an_account_of_another_user_is_not_prefilled(
+    auth_client, user, django_user_model
+):
+    intruder = django_user_model.objects.create_user(username="otro", password="x")
+    foreign = Account.objects.create(
+        owner=intruder, name="Ajena", initial_balance=Decimal("0"), active=True
+    )
+
+    response = auth_client.get(reverse("transfer_create"), {"from_account": foreign.id})
+
+    assert response.context["form"].initial == {}
+
+
+def test_an_inactive_account_is_not_prefilled(auth_client, user):
+    """Las cuentas desactivadas no están en el desplegable: preseleccionar una
+    dejaría el formulario con un valor que no se puede enviar."""
+    closed = Account.objects.create(
+        owner=user, name="Cerrada", initial_balance=Decimal("0"), active=False
+    )
+
+    response = auth_client.get(reverse("transfer_create"), {"to_account": closed.id})
+
+    assert response.context["form"].initial == {}
+
+
+# --------------------------------------------------------------------------
+# La casilla de traspaso no se ofrece al editar
+# --------------------------------------------------------------------------
+
+
+def test_the_checkbox_is_offered_when_creating_an_expense(auth_client, user):
+    response = auth_client.get(reverse("expense_create"))
+
+    assert "id_is_transfer" in response.content.decode()
+
+
+def test_the_checkbox_is_offered_when_creating_an_income(auth_client, user):
+    response = auth_client.get(reverse("income_create"))
+
+    assert "id_is_transfer" in response.content.decode()
+
+
+@pytest.mark.parametrize(
+    "view_name,account_param",
+    [("expense_create", "from_account"), ("income_create", "to_account")],
+)
+def test_the_create_form_tells_the_javascript_where_to_jump(
+    auth_client, user, view_name, account_param
+):
+    """El JS no sabe nada de traspasos: el destino y el papel de la cuenta se los
+    da la plantilla en data-*. Renombrarlos rompería el salto inmediato sin que
+    nada se queje, porque el POST seguiría redirigiendo igual.
+    """
+    response = auth_client.get(reverse(view_name))
+    html = response.content.decode()
+
+    assert f'data-transfer-url="{reverse("transfer_create")}"' in html
+    assert f'data-transfer-account-param="{account_param}"' in html
+    assert "transfer_redirect.js" in html
+
+
+def test_the_checkbox_is_hidden_when_editing_an_expense(
+    auth_client, user, account, category
+):
+    """Editar un gasto no es convertirlo en traspaso: la casilla no pinta nada."""
+    expense = Expense.objects.create(
+        owner=user,
+        account=account,
+        category=category,
+        amount=Decimal("10"),
+        date=date(2024, 5, 11),
+    )
+
+    response = auth_client.get(reverse("expense_edit", args=[expense.pk]))
+
+    assert "id_is_transfer" not in response.content.decode()
+
+
+def test_the_checkbox_is_hidden_when_editing_an_income(auth_client, user, account):
+    income = Income.objects.create(
+        owner=user,
+        account=account,
+        name="Nómina",
+        amount=Decimal("10"),
+        date=date(2024, 5, 11),
+    )
+
+    response = auth_client.get(reverse("income_edit", args=[income.pk]))
+
+    assert "id_is_transfer" not in response.content.decode()
+
+
+def test_posting_is_transfer_while_editing_has_no_effect(
+    auth_client, user, account, category
+):
+    """El campo no está en el formulario, así que mandarlo a mano tampoco cuela."""
+    expense = Expense.objects.create(
+        owner=user,
+        account=account,
+        category=category,
+        amount=Decimal("10"),
+        date=date(2024, 5, 11),
+    )
+
+    auth_client.post(
+        reverse("expense_edit", args=[expense.pk]),
+        {
+            "date": "2024-05-11",
+            "amount": "10",
+            "description": "",
+            "category": category.id,
+            "account": account.id,
+            "is_transfer": "on",
+        },
+    )
+
+    expense.refresh_from_db()
+    assert expense.is_transfer is False
+
+
+def test_a_leg_shows_its_transfer_link_and_no_checkbox(
+    auth_client, user, account, savings
+):
+    """Una pata sigue mandando al traspaso: ni casilla, ni edición suelta."""
+    transfer = make_transfer(user, account, savings)
+
+    listing = auth_client.get(reverse("expense_list"), {"year": 2024})
+    html = listing.content.decode()
+
+    assert reverse("transfer_edit", args=[transfer.pk]) in html
+    assert "id_is_transfer" not in html
+
+    edit = auth_client.get(
+        reverse("expense_edit", args=[transfer.expense_leg_id]), follow=True
+    )
+
+    assert edit.redirect_chain[0][0] == reverse("transfer_edit", args=[transfer.pk])
+    assert "id_is_transfer" not in edit.content.decode()
+
+
+# --------------------------------------------------------------------------
+# Migración de datos: emparejar los traspasos históricos
+# --------------------------------------------------------------------------
+
+
+def link_legacy_transfers():
+    """Lanza la función de la migración 0015 contra los modelos reales."""
+    migration = importlib.import_module("expenses.migrations.0015_link_legacy_transfers")
+    migration.link_legacy_transfers(django_apps, None)
+
+
+def legacy_pair(user, from_account, to_account, category, amount, on):
+    expense = Expense.objects.create(
+        owner=user,
+        account=from_account,
+        category=category,
+        amount=Decimal(amount),
+        date=on,
+        is_transfer=True,
+    )
+    income = Income.objects.create(
+        owner=user,
+        account=to_account,
+        name="Traspaso",
+        amount=Decimal(amount),
+        date=on,
+        is_transfer=True,
+    )
+    return expense, income
+
+
+def test_migration_pairs_an_unambiguous_legacy_transfer(
+    user, account, savings, category
+):
+    expense, income = legacy_pair(
+        user, account, savings, category, "200", date(2024, 5, 11)
+    )
+
+    link_legacy_transfers()
+
+    transfer = Transfer.objects.get()
+    assert transfer.expense_leg_id == expense.pk
+    assert transfer.income_leg_id == income.pk
+    assert transfer.from_account_id == account.pk
+    assert transfer.to_account_id == savings.pk
+    assert transfer.amount == Decimal("200")
+    assert transfer.date == date(2024, 5, 11)
+    assert transfer.fee_amount is None
+
+
+def test_migration_leaves_ambiguous_candidates_alone(user, account, savings, category):
+    # Dos gastos y dos ingresos con el mismo importe y fecha: no hay forma de
+    # saber cuál va con cuál, así que no se toca ninguno.
+    legacy_pair(user, account, savings, category, "200", date(2024, 5, 11))
+    legacy_pair(user, account, savings, category, "200", date(2024, 5, 11))
+
+    link_legacy_transfers()
+
+    assert Transfer.objects.count() == 0
+    assert Expense.objects.filter(is_transfer=True).count() == 2
+    assert Income.objects.filter(is_transfer=True).count() == 2
+
+
+def test_migration_leaves_orphans_alone(user, account, category):
+    Expense.objects.create(
+        owner=user,
+        account=account,
+        category=category,
+        amount=Decimal("200"),
+        date=date(2024, 5, 11),
+        is_transfer=True,
+    )
+
+    link_legacy_transfers()
+
+    assert Transfer.objects.count() == 0
+    assert Expense.objects.filter(is_transfer=True).count() == 1
+
+
+def test_migration_ignores_normal_movements(user, account, savings, category):
+    Expense.objects.create(
+        owner=user,
+        account=account,
+        category=category,
+        amount=Decimal("200"),
+        date=date(2024, 5, 11),
+    )
+    Income.objects.create(
+        owner=user,
+        account=savings,
+        name="Nómina",
+        amount=Decimal("200"),
+        date=date(2024, 5, 11),
+    )
+
+    link_legacy_transfers()
+
+    assert Transfer.objects.count() == 0
+
+
+def test_migration_skips_a_pair_on_the_same_account(user, account, category):
+    legacy_pair(user, account, account, category, "200", date(2024, 5, 11))
+
+    link_legacy_transfers()
+
+    assert Transfer.objects.count() == 0
+
+
+def test_migration_does_not_cross_owners(user, account, category, django_user_model):
+    other = django_user_model.objects.create_user(username="otro", password="x")
+    other_account = Account.objects.create(
+        owner=other, name="Suya", initial_balance=Decimal("0"), active=True
+    )
+
+    Expense.objects.create(
+        owner=user,
+        account=account,
+        category=category,
+        amount=Decimal("200"),
+        date=date(2024, 5, 11),
+        is_transfer=True,
+    )
+    Income.objects.create(
+        owner=other,
+        account=other_account,
+        name="Traspaso",
+        amount=Decimal("200"),
+        date=date(2024, 5, 11),
+        is_transfer=True,
+    )
+
+    link_legacy_transfers()
+
+    assert Transfer.objects.count() == 0
+
+
+def test_migration_is_idempotent(user, account, savings, category):
+    legacy_pair(user, account, savings, category, "200", date(2024, 5, 11))
+
+    link_legacy_transfers()
+    link_legacy_transfers()
+
+    assert Transfer.objects.count() == 1
+
+
+def test_migration_does_not_touch_legs_of_an_existing_transfer(user, account, savings):
+    make_transfer(user, account, savings)
+
+    link_legacy_transfers()
+
+    assert Transfer.objects.count() == 1

expenses_manager/expenses/tests/test_transfers.py

@@ -203,7 +203,12 @@ def test_account_list_balance_counts_the_transfer(auth_client, user, account, ca
 # Formularios
 # --------------------------------------------------------------------------
 
-def test_expense_form_can_mark_a_transfer(auth_client, user, account, category):
+# Marcar la casilla ya no guarda un movimiento marcado: reconduce al formulario de
+# traspaso, que crea las dos patas. El detalle está en test_transfer_model.py.
+
+def test_marking_the_expense_form_as_transfer_creates_nothing(
+    auth_client, user, account, category
+):
     response = auth_client.post(
         reverse("expense_create"),
         {
@@ -217,10 +222,13 @@ def test_expense_form_can_mark_a_transfer(auth_client, user, account, category):
     )
 
     assert response.status_code == 302
-    assert Expense.objects.get(owner=user).is_transfer is True
+    assert reverse("transfer_create") in response.url
+    assert not Expense.objects.filter(owner=user).exists()
 
 
-def test_income_form_can_mark_a_transfer(auth_client, user, account):
+def test_marking_the_income_form_as_transfer_creates_nothing(
+    auth_client, user, account
+):
     response = auth_client.post(
         reverse("income_create"),
         {
@@ -233,7 +241,8 @@ def test_income_form_can_mark_a_transfer(auth_client, user, account):
     )
 
     assert response.status_code == 302
-    assert Income.objects.get(owner=user).is_transfer is True
+    assert reverse("transfer_create") in response.url
+    assert not Income.objects.filter(owner=user).exists()
 
 
 def test_expense_defaults_to_not_a_transfer(user, account, category):

expenses_manager/expenses/urls.py

@@ -25,6 +25,10 @@ urlpatterns = [
     path('fuel/create/', views.fuel_create, name='fuel_create'),
     path('fuel/<int:pk>/edit/', views.fuel_edit, name='fuel_edit'),
     path('fuel/<int:pk>/delete/', views.fuel_delete, name='fuel_delete'),
+    path('transfers/', views.transfer_list, name='transfer_list'),
+    path('transfers/new/', views.transfer_create, name='transfer_create'),
+    path('transfers/<int:pk>/edit/', views.transfer_edit, name='transfer_edit'),
+    path('transfers/<int:pk>/delete/', views.transfer_delete, name='transfer_delete'),
     path('categories/', views.category_list, name='category_list'),
     path('categories/<int:pk>/edit/', views.category_edit, name='category_edit'),
     path('categories/<int:pk>/delete/', views.category_delete, name='category_delete'),

expenses_manager/expenses/views.py

@@ -1,9 +1,19 @@
 import logging
 import calendar
 from datetime import date, datetime, timedelta
+from urllib.parse import urlencode
 from decimal import Decimal
 from django.contrib import messages
-from .models import Account, Category, Expense, FuelEntry, Tag, Income, Goal
+from .models import (
+    Account,
+    Category,
+    Expense,
+    FuelEntry,
+    Tag,
+    Income,
+    Goal,
+    Transfer,
+)
 from .forms import (
     ExpenseForm,
     IncomeForm,
@@ -12,6 +22,7 @@ from .forms import (
     FuelEntryForm,
     CategoryForm,
     GoalForm,
+    TransferForm,
 )
 
 from django.core.paginator import Paginator
@@ -27,6 +38,7 @@ from django.db.models.functions import (
 from django.contrib.auth.decorators import login_required
 from django.utils.http import url_has_allowed_host_and_scheme
 from django.shortcuts import get_object_or_404, render, redirect
+from django.urls import reverse
 
 logger = logging.getLogger(__name__)
 
@@ -37,11 +49,6 @@ def _get_int(value):
         return None
 
 
-# Umbral del eje del gráfico con rango libre: dos meses es donde un gráfico
-# diario deja de leerse, así que por encima se agrupa por mes.
-RANGE_DAY_CHART_MAX_DAYS = 62
-
-
 def _get_date(value):
     """Parsea una fecha AAAA-MM-DD de la URL. None si falta o no es válida."""
     try:
@@ -50,6 +57,25 @@ def _get_date(value):
         return None
 
 
+def _get_decimal(value):
+    """Parsea un importe de la URL. None si falta o no es un número usable.
+
+    Se descartan NaN e Infinity aparte: Decimal los acepta pero luego revientan
+    en cuanto se comparan o se guardan.
+    """
+    try:
+        number = Decimal(value)
+    except (TypeError, ValueError, ArithmeticError):
+        return None
+
+    return number if number.is_finite() else None
+
+
+# Umbral del eje del gráfico con rango libre: dos meses es donde un gráfico
+# diario deja de leerse, así que por encima se agrupa por mes.
+RANGE_DAY_CHART_MAX_DAYS = 62
+
+
 def _resolve_date_range(request):
     """Lee el rango de fechas libre de la URL.
 
@@ -128,6 +154,88 @@ def _analysis_expenses(user):
     return Expense.objects.filter(owner=user).exclude(is_transfer=True)
 
 
+def _reject_transfer_leg(request, movement):
+    """Corta la edición o el borrado suelto de una pata de traspaso.
+
+    Devuelve un redirect a la edición del traspaso, o None si el movimiento es
+    normal y se puede tocar. Las patas las mantiene cuadradas Transfer.sync(),
+    así que tocar una por separado descuadraría la otra sin que nada lo avise:
+    es justo el problema que el modelo Transfer viene a resolver.
+
+    Los listados ya no enseñan esos enlaces, pero la URL sigue ahí a mano.
+    """
+    transfer = movement.transfer
+
+    if transfer is None:
+        return None
+
+    messages.error(
+        request,
+        "Este movimiento forma parte de un traspaso. Edítalo o bórralo desde el "
+        "traspaso para que las dos cuentas sigan cuadradas.",
+    )
+    return redirect("transfer_edit", pk=transfer.pk)
+
+
+def _transfer_create_url(data, account_param):
+    """URL de "nuevo traspaso" arrastrando lo que ya se hubiera escrito.
+
+    `data` es el POST de un formulario de gasto o de ingreso y `account_param` el
+    papel que juega su cuenta en el traspaso: "from_account" si viene de un gasto
+    (el dinero sale de ahí) y "to_account" si viene de un ingreso.
+
+    Lo que no se pueda interpretar se deja fuera: el formulario de traspaso saldrá
+    con ese campo vacío, que es mejor que un error por un dato a medio escribir.
+    """
+    params = {}
+
+    if (date_value := _get_date(data.get("date"))) is not None:
+        params["date"] = date_value.isoformat()
+
+    if (amount := _get_decimal(data.get("amount"))) is not None:
+        params["amount"] = str(amount)
+
+    if (account_id := _get_int(data.get("account"))) is not None:
+        params[account_param] = account_id
+
+    url = reverse("transfer_create")
+    return f"{url}?{urlencode(params)}" if params else url
+
+
+def _transfer_initial(request):
+    """Datos de arranque del formulario de traspaso leídos de la URL.
+
+    Los manda el formulario de gasto o de ingreso cuando el usuario marca la
+    casilla de traspaso. Nada de esto es de fiar (es la URL): lo que no se pueda
+    interpretar se ignora y el campo sale vacío.
+    """
+    initial = {}
+
+    if (date_value := _get_date(request.GET.get("date"))) is not None:
+        initial["date"] = date_value
+
+    if (amount := _get_decimal(request.GET.get("amount"))) is not None:
+        initial["amount"] = amount
+
+    # Las cuentas se comprueban contra las del usuario: un id ajeno o de una
+    # cuenta desactivada no se preselecciona aunque venga en la URL.
+    wanted = {
+        field: account_id
+        for field in ("from_account", "to_account")
+        if (account_id := _get_int(request.GET.get(field))) is not None
+    }
+
+    if wanted:
+        own = set(
+            Account.objects.filter(
+                owner=request.user, active=True, pk__in=wanted.values()
+            ).values_list("pk", flat=True)
+        )
+        initial.update({f: pk for f, pk in wanted.items() if pk in own})
+
+    return initial
+
+
 def _account_balances(accounts):
     """Calcula el saldo de cada cuenta con dos queries agregadas (nada de
     account.current_balance() en bucle, que dispararía N+1).
@@ -353,7 +461,11 @@ def home(request):
 
 @login_required
 def expense_list(request):
-    expenses = Expense.objects.filter(owner=request.user)
+    # Las relaciones de traspaso van en select_related porque la tabla consulta
+    # expense.transfer en cada fila para decidir los enlaces de acción.
+    expenses = Expense.objects.filter(owner=request.user).select_related(
+        "transfer_out", "transfer_fee"
+    )
 
     categories = Category.objects.filter(owner=request.user)
 
@@ -483,6 +595,13 @@ def expense_list(request):
 @login_required
 def expense_create(request):
     if request.method == "POST":
+        # Marcado como traspaso: esto no se guarda aquí. Un traspaso son dos patas
+        # que crea Transfer.sync(), así que se reconduce al formulario de traspaso
+        # con lo que ya hubiera escrito. Se mira el POST en bruto y antes de
+        # validar porque el gasto puede estar a medias y da igual: no se crea.
+        if request.POST.get("is_transfer"):
+            return redirect(_transfer_create_url(request.POST, "from_account"))
+
         form = ExpenseForm(request.POST, user=request.user)
         if form.is_valid():
             expense = form.save(commit=False)
@@ -510,6 +629,10 @@ def expense_edit(request, pk):
         owner=request.user,
     )
 
+    blocked = _reject_transfer_leg(request, expense)
+    if blocked:
+        return blocked
+
     if request.method == "POST":
         form = ExpenseForm(request.POST or None, instance=expense, user=request.user)
 
@@ -538,6 +661,10 @@ def expense_delete(request, pk):
         owner=request.user,
     )
 
+    blocked = _reject_transfer_leg(request, expense)
+    if blocked:
+        return blocked
+
     if request.method == "POST":
         expense.delete()
         messages.success(request, "Gasto eliminado correctamente.")
@@ -967,6 +1094,11 @@ def account_delete(request, pk):
 @login_required
 def income_create(request):
     if request.method == "POST":
+        # Igual que en expense_create, pero la cuenta es el destino: el dinero
+        # entra en ella.
+        if request.POST.get("is_transfer"):
+            return redirect(_transfer_create_url(request.POST, "to_account"))
+
         form = IncomeForm(request.POST, user=request.user)
         if form.is_valid():
             income = form.save(commit=False)
@@ -984,7 +1116,9 @@ def income_create(request):
 
 @login_required
 def income_list(request):
-    incomes = Income.objects.filter(owner=request.user).select_related("account")
+    incomes = Income.objects.filter(owner=request.user).select_related(
+        "account", "transfer_in"
+    )
 
     year_list = Income.objects.filter(owner=request.user).dates("date", "year")
 
@@ -1064,6 +1198,10 @@ def income_list(request):
 def income_edit(request, pk):
     income = get_object_or_404(Income, pk=pk, owner=request.user)
 
+    blocked = _reject_transfer_leg(request, income)
+    if blocked:
+        return blocked
+
     if request.method == "POST":
         form = IncomeForm(request.POST, instance=income, user=request.user)
         if form.is_valid():
@@ -1082,6 +1220,10 @@ def income_edit(request, pk):
 def income_delete(request, pk):
     income = get_object_or_404(Income, pk=pk, owner=request.user)
 
+    blocked = _reject_transfer_leg(request, income)
+    if blocked:
+        return blocked
+
     if request.method == "POST":
         income.delete()
         messages.success(request, "Ingreso eliminado.")
@@ -1306,6 +1448,14 @@ def category_delete(request, pk):
     category = get_object_or_404(Category, pk=pk, owner=request.user)
     
     if request.method == "POST":
+        if category.is_system:
+            messages.error(
+                request,
+                f"No se puede eliminar «{category.name}»; la usa la aplicación para "
+                "clasificar los traspasos y sus comisiones."
+            )
+            return redirect("category_list")
+
         try:
             category.delete()
         except ProtectedError:
@@ -1428,3 +1578,92 @@ def goal_delete(request, pk):
 @login_required
 def settings_index(request):
     return render(request, "settings/index.html", {"active_menu": "settings"})
+
+
+@login_required
+def transfer_list(request):
+    transfers = Transfer.objects.filter(owner=request.user).select_related(
+        "from_account", "to_account"
+    )
+
+    return render(
+        request,
+        "transfers/list.html",
+        {
+            "active_menu": "transfers",
+            "transfers": transfers,
+        },
+    )
+
+
+@login_required
+def transfer_create(request):
+    if request.method == "POST":
+        form = TransferForm(request.POST, user=request.user)
+
+        if form.is_valid():
+            transfer = form.save(commit=False)
+            transfer.owner = request.user
+            # sync() guarda el traspaso y crea las patas en una sola transacción.
+            transfer.sync()
+
+            messages.success(request, "Traspaso creado.")
+            return redirect("transfer_list")
+    else:
+        # La URL puede traer fecha, importe y cuenta del formulario de gasto o de
+        # ingreso del que se venga.
+        form = TransferForm(user=request.user, initial=_transfer_initial(request))
+
+    return render(
+        request,
+        "transfers/form.html",
+        {
+            "active_menu": "transfers",
+            "form": form,
+            "title": "Nuevo traspaso",
+        },
+    )
+
+
+@login_required
+def transfer_edit(request, pk):
+    transfer = get_object_or_404(Transfer, pk=pk, owner=request.user)
+
+    if request.method == "POST":
+        form = TransferForm(request.POST, instance=transfer, user=request.user)
+
+        if form.is_valid():
+            transfer = form.save(commit=False)
+            transfer.sync()
+
+            messages.success(request, "Traspaso actualizado.")
+            return redirect("transfer_list")
+    else:
+        form = TransferForm(instance=transfer, user=request.user)
+
+    return render(
+        request,
+        "transfers/form.html",
+        {
+            "active_menu": "transfers",
+            "form": form,
+            "title": "Editar traspaso",
+        },
+    )
+
+
+@login_required
+def transfer_delete(request, pk):
+    transfer = get_object_or_404(Transfer, pk=pk, owner=request.user)
+
+    if request.method == "POST":
+        # Transfer.delete() se lleva también las dos patas y la comisión.
+        transfer.delete()
+        messages.success(request, "Traspaso eliminado.")
+        return redirect("transfer_list")
+
+    return render(
+        request,
+        "transfers/confirm_delete.html",
+        {"active_menu": "transfers", "transfer": transfer},
+    )