diff --git a/eo_gestion/eo_facture/admin.py b/eo_gestion/eo_facture/admin.py
index f286d7c..28c6538 100644
--- a/eo_gestion/eo_facture/admin.py
+++ b/eo_gestion/eo_facture/admin.py
@@ -24,11 +24,12 @@ from django.conf.urls import url
 from django.contrib import admin
 from django.contrib.admin.options import BaseModelAdmin
 from django.contrib.humanize.templatetags.humanize import ordinal
+from django.db import transaction
 from django.db.models import TextField
 from django.forms import Textarea
 from django.forms.models import BaseInlineFormSet
 from django.shortcuts import render
-from django.urls import reverse
+from django.urls import path, reverse
 from django.utils.html import format_html
 from django.utils.six import BytesIO
 
@@ -224,12 +225,66 @@ class ContratAdmin(LookupAllowed, admin.ModelAdmin):
 
         return render(request, "admin/eo_facture/contrat/duplicate.html", context=context)
 
+    def facturer_echeance(self, request, object_id):
+        if request.method != 'POST':
+            raise http.Http404
+
+        contrat = self.get_object(request, object_id)
+
+        assert contrat.periodicite
+
+        echeance = int(request.POST['echeance'])
+
+        numero = None
+        for i, debut, _ in contrat.periodicite_echeances():
+            if i == echeance:
+                numero = i
+                break
+
+        assert numero is not None
+
+        with transaction.atomic():
+            facture, _ = models.Facture.objects.update_or_create(
+                client=contrat.client,
+                contrat=contrat,
+                echeance=debut,
+                numero_d_echeance=numero,
+                defaults={
+                    'creator': request.user,
+                    'numero_d_echeance': numero,
+                },
+            )
+            if facture.proforma:
+                facture.intitule = f'{contrat.intitule} {facture.periode}'
+            facture.clean()
+            facture.save()
+            facture.import_ligne()
+
+        return http.HttpResponseRedirect(reverse('admin:eo_facture_facture_change', args=(facture.id,)))
+
     def get_urls(self):
         urls = super().get_urls()
         duplicate_view = self.admin_site.admin_view(self.duplicate)
-        my_urls = [url(r'^(.+)/duplicate/$', duplicate_view, name='eo_facture_contrat_duplicate')]
+        facturer_echeance_view = self.admin_site.admin_view(self.facturer_echeance)
+        my_urls = [
+            url(r'^(.+)/duplicate/$', duplicate_view, name='eo_facture_contrat_duplicate'),
+            path(
+                '<path:object_id>/facturer-echeance/',
+                facturer_echeance_view,
+                name='eo_facture_contrat_facturer_echeance',
+            ),
+        ]
         return my_urls + urls
 
+    def get_fields(self, request, obj=None):
+        fields = list(super().get_fields(request, obj=obj))
+        if obj:
+            if obj.periodicite:
+                fields = [field for field in fields if field != 'percentage_per_year']
+            elif obj.percentage_per_year and len(obj.percentage_per_year) > 1:
+                fields = [field for field in fields if field != 'periodicite']
+        return fields
+
 
 def index(facture):
     return format_html('{0}', ordinal(facture.index()))
@@ -272,7 +327,7 @@ class FactureAdmin(LookupAllowed, admin.ModelAdmin):
         'montant_ttc',
         'account_on_previous_period',
     ]
-    readonly_fields = ['creator', 'solde', 'ordre', 'montant', 'montant_ttc']
+    readonly_fields = ['creator', 'solde', 'ordre', 'montant', 'montant_ttc', 'periode']
     date_hierarchy = 'emission'
     list_select_related = True
     save_on_top = True
@@ -296,6 +351,12 @@ class FactureAdmin(LookupAllowed, admin.ModelAdmin):
 
     column_solde.short_description = 'Solde'
 
+    def has_delete_permission(self, request, obj=None):
+        # ne pas supprimer les factures émises
+        if obj and not obj.proforma:
+            return False
+        return super().has_delete_permission(request, obj=obj)
+
     def get_queryset(self, request):
         from django.db import connection
 
@@ -396,8 +457,9 @@ class FactureAdmin(LookupAllowed, admin.ModelAdmin):
         return my_urls + urls
 
     def show_client(self, obj):
-        url = reverse('admin:eo_facture_client_change', args=[obj.client.id])
-        return format_html('<a href="{0}">{1}</a>', url, obj.client)
+        if obj.client:
+            url = reverse('admin:eo_facture_client_change', args=[obj.client.id])
+            return format_html('<a href="{0}">{1}</a>', url, obj.client)
 
     show_client.short_description = 'Client'
 
@@ -431,6 +493,18 @@ class FactureAdmin(LookupAllowed, admin.ModelAdmin):
         changelist.pk_attname = 'pk_or_code'
         return changelist
 
+    def get_fields(self, request, obj=None):
+        fields = list(super().get_fields(request, obj=obj))
+        if not obj or not obj.contrat or obj.contrat.periodicite:
+            fields += ['numero_d_echeance', 'periode']
+        return fields
+
+    def get_readonly_fields(self, request, obj=None):
+        fields = list(super().get_readonly_fields(request, obj=obj))
+        if obj and obj.contrat and obj.contrat.periodicite:
+            fields += ['periode']
+        return fields
+
 
 class PaymentAdmin(LookupAllowed, admin.ModelAdmin, CommonPaymentInline):
     form = forms.PaymentForm
diff --git a/eo_gestion/eo_facture/forms.py b/eo_gestion/eo_facture/forms.py
index 54689ba..c062859 100644
--- a/eo_gestion/eo_facture/forms.py
+++ b/eo_gestion/eo_facture/forms.py
@@ -165,18 +165,19 @@ class FactureForm(forms.ModelForm):
         # réinitialiser la date d'émission quand une facture quitte le statut
         # proforma, sauf si une date d'émission spécifique a été fixée à la
         # main
+        cleaned_data = super().clean()
         update_echeance = False
         if self.instance.proforma and 'proforma' in self.changed_data and 'emission' not in self.changed_data:
-            self.cleaned_data['emission'] = models.today()
+            cleaned_data['emission'] = models.today()
             update_echeance = True
         if (
-            self.cleaned_data.get('emission')
+            cleaned_data.get('emission')
             and 'emission' in self.changed_data
             and 'echeance' not in self.changed_data
         ):
             update_echeance = True
         if update_echeance:
-            self.cleaned_data['echeance'] = self.cleaned_data['emission'] + datetime.timedelta(
+            cleaned_data['echeance'] = cleaned_data['emission'] + datetime.timedelta(
                 days=models.DELAI_PAIEMENT
             )
 
diff --git a/eo_gestion/eo_facture/migrations/0015_add_fields_for_periodic_invoicing.py b/eo_gestion/eo_facture/migrations/0015_add_fields_for_periodic_invoicing.py
new file mode 100644
index 0000000..6734abf
--- /dev/null
+++ b/eo_gestion/eo_facture/migrations/0015_add_fields_for_periodic_invoicing.py
@@ -0,0 +1,43 @@
+# Generated by Django 2.2.24 on 2021-11-20 17:31
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('eo_facture', '0014_facture_annulation'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='contrat',
+            name='periodicite',
+            field=models.CharField(
+                blank=True,
+                choices=[('annuelle', 'Annuelle'), ('semestrielle', 'Semestrielle')],
+                max_length=16,
+                null=True,
+                verbose_name='Périodicité',
+            ),
+        ),
+        migrations.AddField(
+            model_name='contrat',
+            name='periodicite_debut',
+            field=models.DateField(blank=True, null=True, verbose_name='Périodicité début'),
+        ),
+        migrations.AddField(
+            model_name='contrat',
+            name='periodicite_fin',
+            field=models.DateField(blank=True, null=True, verbose_name='Périodicité fin'),
+        ),
+        migrations.AddField(
+            model_name='facture',
+            name='numero_d_echeance',
+            field=models.IntegerField(blank=True, null=True, verbose_name="Numéro d'échéance"),
+        ),
+        migrations.AlterUniqueTogether(
+            name='facture',
+            unique_together={('contrat', 'numero_d_echeance')},
+        ),
+    ]
diff --git a/eo_gestion/eo_facture/models.py b/eo_gestion/eo_facture/models.py
index b7b6e69..bce7530 100644
--- a/eo_gestion/eo_facture/models.py
+++ b/eo_gestion/eo_facture/models.py
@@ -16,15 +16,17 @@
 
 
 import datetime
+import itertools
 import os.path
 from collections import defaultdict
 from decimal import ROUND_HALF_UP, Decimal
 
+from dateutil.relativedelta import relativedelta
 from django.conf import settings
 from django.contrib.auth import get_user_model
 from django.core.exceptions import ValidationError
 from django.core.validators import RegexValidator, validate_email
-from django.db import models
+from django.db import models, transaction
 from django.db.models import F, Q, Sum
 from django.db.models.query import QuerySet
 from django.db.models.signals import post_delete, post_save
@@ -119,11 +121,26 @@ class Contrat(models.Model):
     tva = models.DecimalField(max_digits=8, decimal_places=2, default=Decimal(DEFAULT_TVA))
     creation = models.DateField(default=today)
     creator = models.ForeignKey(User, verbose_name='Créateur', on_delete=models.CASCADE)
-    percentage_per_year = fields.PercentagePerYearField(default=one_hundred_percent_this_year)
+    percentage_per_year = fields.PercentagePerYearField(
+        default=one_hundred_percent_this_year, verbose_name='Pourcentage par année'
+    )
     montant_sous_traite = models.DecimalField(max_digits=8, decimal_places=2, default=Decimal('0'))
     image = models.ImageField('Image', upload_to='images/', blank=True, null=True)
     numero_marche = models.CharField(max_length=128, verbose_name='Numéro du marché', blank=True, default='')
 
+    periodicite = models.CharField(
+        verbose_name='Périodicité',
+        max_length=16,
+        choices=[
+            ('annuelle', 'Annuelle'),
+            ('semestrielle', 'Semestrielle'),
+        ],
+        blank=True,
+        null=True,
+    )
+    periodicite_debut = models.DateField(verbose_name='Périodicité début', blank=True, null=True)
+    periodicite_fin = models.DateField(verbose_name='Périodicité fin', blank=True, null=True)
+
     tags = taggit.TaggableManager(blank=True)
 
     def montant_facture(self):
@@ -156,6 +173,73 @@ class Contrat(models.Model):
     def clean(self):
         self.numero_marche = self.numero_marche.strip()
 
+        if self.periodicite and not self.periodicite_debut:
+            raise ValidationError(
+                {'periodicite_debut': 'Vous devez définir une date de début pour la période.'}
+            )
+        if self.periodicite_debut and not self.periodicite:
+            raise ValidationError({'periodicite': 'Vous devez définir une périodicité.'})
+
+        if self.periodicite_fin and not self.periodicite:
+            raise ValidationError({'periodicite': 'Vous devez définir une périodicité.'})
+
+        if self.periodicite and len(self.percentage_per_year) > 1:
+            raise ValidationError(
+                'Vous ne pouvez pas utiliser pourcentage par année en même temps que périodicité.'
+            )
+
+    @property
+    def periodicite_duration(self):
+        if self.periodicite == 'annuelle':
+            return relativedelta(years=1)
+
+        if self.periodicite == 'semestrielle':
+            return relativedelta(months=6)
+
+        raise ValueError
+
+    def periodicite_dates(self):
+        if self.periodicite == 'annuelle':
+            durations = (relativedelta(years=i) for i in itertools.count())
+        elif self.periodicite == 'semestrielle':
+            durations = (relativedelta(months=6 * i) for i in itertools.count())
+        else:
+            raise ValueError('aucune échéance')
+        dates = (self.periodicite_debut + duration for duration in durations)
+        if self.periodicite_fin:
+            return itertools.takewhile(lambda date: date < self.periodicite_fin, dates)
+        else:
+            return dates
+
+    def periodicite_nombre_d_echeances(self):
+        if not self.periodicite_fin:
+            return '*'
+        return len(list(self.periodicite_echeances(limit=1000)))
+
+    def periodicite_echeances(self, until=None, limit=3):
+        i = 1
+        count = 0
+        n = now().date()
+        for day in self.periodicite_dates():
+            if until and until < day:
+                break
+            periode_fin = day + self.periodicite_duration
+            if self.periodicite_fin and periode_fin > self.periodicite_fin:
+                break
+            if day > n:
+                count += 1
+            yield i, day, periode_fin
+            i += 1
+            if count == limit:
+                break
+
+    def save(self, *args, **kwargs):
+        with transaction.atomic(savepoint=False):
+            if not self.periodicite:
+                # supprimer les échéances des factures si pas de periodicite
+                self.factures.update(numero_d_echeance=None)
+            return super().save(*args, **kwargs)
+
     def __str__(self):  # pylint: disable=invalid-str-returned
         return self.intitule
 
@@ -257,6 +341,11 @@ class Facture(models.Model):
         verbose_name='Notes privées',
         help_text='À usage purement interne, ne seront jamais présentes sur la facture',
     )
+    numero_d_echeance = models.IntegerField(
+        verbose_name='Numéro d\'échéance',
+        blank=True,
+        null=True,
+    )
 
     objects = FactureQuerySet.as_manager()
 
@@ -300,9 +389,30 @@ class Facture(models.Model):
                     raise ValidationError("Le client de la facture et du contrat doivent être identiques.")
             else:
                 self.client = self.contrat.client
+            if self.contrat.periodicite:
+                if self.numero_d_echeance is None:
+                    raise ValidationError(
+                        {
+                            'numero_d_echeance': 'Vous devez définir un numéro d\'échéance car le contrat est périodique.'
+                        }
+                    )
+                for i, dummy, dummy in self.contrat.periodicite_echeances():
+                    if i == self.numero_d_echeance:
+                        break
+                else:
+                    raise ValidationError('Numéro d\'échéance invalide')
+            else:
+                if self.numero_d_echeance is not None:
+                    raise ValidationError(
+                        'Un numéro d\'échéance ne peut être défini que pour un contrat récurrent.'
+                    )
         else:
             if not self.intitule:
                 raise ValidationError("La facture doit avoir un intitulé")
+            if self.numero_d_echeance is not None:
+                raise ValidationError(
+                    'Un numéro d\'échéance ne peut être défini que pour un contrat récurrent.'
+                )
         if not self.proforma:
             try:
                 for ligne in self.lignes.all():
@@ -444,8 +554,36 @@ class Facture(models.Model):
         filename = f'{self.code()}-{self.client.nom}{avoir}.pdf'
         return filename
 
+    @transaction.atomic(savepoint=False)
+    def import_ligne(self):
+        for prestation in self.contrat.prestations.all():
+            ligne, _ = Ligne.objects.update_or_create(
+                facture=self,
+                intitule=prestation.intitule,
+                defaults={
+                    'prix_unitaire_ht': prestation.prix_unitaire_ht,
+                    'quantite': prestation.quantite,
+                },
+            )
+            ligne.clean()
+
+    def periode(self):
+        if self.contrat and self.contrat.periodicite and self.numero_d_echeance is not None:
+            for i, debut, fin in self.contrat.periodicite_echeances():
+                if i == self.numero_d_echeance:
+                    debut = debut.strftime('%d/%m/%Y')
+                    fin = fin.strftime('%d/%m/%Y')
+                    return f'du {debut} au {fin}'
+
+    periode.short_description = 'Dates de l\'échéance'
+
+    periode = property(periode)
+
     class Meta:
         ordering = ("-id",)
+        unique_together = [
+            ('contrat', 'numero_d_echeance'),
+        ]
 
 
 class Ligne(models.Model):
diff --git a/eo_gestion/eo_facture/templates/admin/eo_facture/contrat/change_form.html b/eo_gestion/eo_facture/templates/admin/eo_facture/contrat/change_form.html
index 4e42b9e..0203ed3 100644
--- a/eo_gestion/eo_facture/templates/admin/eo_facture/contrat/change_form.html
+++ b/eo_gestion/eo_facture/templates/admin/eo_facture/contrat/change_form.html
@@ -6,11 +6,29 @@
   {% url opts|admin_urlname:'history' original.pk|admin_urlquote as history_url %}
   <ul class="object-tools"><li><a href="{{ history_url }}" class="historylink">{% trans "History" %}</a></li>
   {% if has_absolute_url %}<li><a href="../../../r/{{ content_type_id }}/{{ object_id }}/" class="viewsitelink">{% trans "View on site" %}</a></li>{% endif%}
+  {% if not original.periodicite %}
   <li><a href="{% url "admin:eo_facture_contrat_duplicate" original.id %}">Dupliquer</a></li>
+  {% endif %}
   <li><a href="{% url "admin:eo_facture_facture_changelist" %}?contrat={{ original.id }}">Factures</a></li>
+  {% if not original.periodicite %}
   <li><a href="{% url "admin:eo_facture_facture_add" %}?contrat={{ original.id }}&client={{ original.client.id }}&taux_tva={{ original.tva }}">Ajouter une facture</a></li>
   <li><a href="{% url "admin:eo_facture_facture_add_simple" %}?contrat={{ original.id }}">Ajouter une facture comme pourcentage du total</a></li>
+  {% endif %}
   </ul>
 {% endif %}{% endif %}
 {% endblock %}
 
+{% block after_field_sets %}
+{% if original.periodicite and original.periodicite_debut %}
+<fieldset class="module">
+    <h2>Échéances</h2>
+    <div>
+        <ul>
+            {% for echeance in original.periodicite_echeances %}
+                <li>du {{ echeance.1 }} au {{ echeance.2 }}</li>
+            {% endfor %}
+        </ul>
+    </div>
+</fieldset>
+{% endif %}
+{% endblock %}
diff --git a/eo_gestion/eo_facture/templates/admin/eo_facture/facture/change_form.html b/eo_gestion/eo_facture/templates/admin/eo_facture/facture/change_form.html
index b6063d0..13b1b51 100644
--- a/eo_gestion/eo_facture/templates/admin/eo_facture/facture/change_form.html
+++ b/eo_gestion/eo_facture/templates/admin/eo_facture/facture/change_form.html
@@ -6,7 +6,9 @@
 <ul class="object-tools">
 	{% url opts|admin_urlname:'history' original.pk|admin_urlquote as history_url %}
 	<li><a href="{{ history_url }}" class="historylink">{% trans "History" %}</a></li>
+    {% if original.client %}
 	<li><a href="{% url "admin:eo_facture_client_change" original.client.id %}" class="historylink">Client</a></li>
+    {% endif %}
 	{% if original.contrat %}
 	<li><a href="{% url "admin:eo_facture_contrat_change" original.contrat.id %}" class="historylink">Contrat</a></li>
 	{% endif %}
diff --git a/eo_gestion/eo_facture/templates/eo_facture/echeances.html b/eo_gestion/eo_facture/templates/eo_facture/echeances.html
new file mode 100644
index 0000000..782a830
--- /dev/null
+++ b/eo_gestion/eo_facture/templates/eo_facture/echeances.html
@@ -0,0 +1,38 @@
+{% load eo_facture %}
+{% if echeances %}
+<div class="module" id="echeances">
+<h2>Contrats récurrents à facturer</h2>
+
+<table class="table">
+    <thead>
+        <th class="debut">Date anniversaire</th>
+        <th class="client">Client</th>
+        <th class="contrat">Contrat</th>
+        <th class="occurence">Échéance</th>
+        <th class="periodicite">Périodicité</th>
+        <th></th>
+    </thead>
+    <tbody>
+    {% for echeance in echeances %}
+    <tr>
+        <td class="debut">{{ echeance.debut }} - {{ echeance.fin }}</td>
+        <th class="client"><a href="{% url "admin:eo_facture_client_change" echeance.contrat.client.id %}">{{ echeance.contrat.client }}</a></th>
+        <td class="contrat">
+            <a href="{% url "admin:eo_facture_contrat_change" echeance.contrat.id %}">
+            {{ echeance.contrat.intitule }}
+            <a/>
+        </td>
+        <td class="occurence">{{ echeance.occurrence }} / {{ echeance.contrat.periodicite_nombre_d_echeances }}</td>
+        <td class="periodicite">{{ echeance.contrat.get_periodicite_display }}</td>
+        <td>
+            <form method="post" action="{% url "admin:eo_facture_contrat_facturer_echeance" echeance.contrat.id %}">
+                {% csrf_token %}
+                <input type="hidden" name="echeance" value="{{ echeance.occurrence }}"/>
+                <input type="submit" value="Facturer" style="padding: 2px 3px"/>
+            </form>
+        </td>
+    </tr>
+    {% endfor %}
+</table>
+</div>
+{% endif %}
diff --git a/eo_gestion/eo_facture/templatetags/eo_facture.py b/eo_gestion/eo_facture/templatetags/eo_facture.py
index ff7c94f..c181a36 100644
--- a/eo_gestion/eo_facture/templatetags/eo_facture.py
+++ b/eo_gestion/eo_facture/templatetags/eo_facture.py
@@ -19,6 +19,7 @@ from collections import defaultdict
 from datetime import date, datetime, timedelta
 from decimal import Decimal, InvalidOperation
 
+from dateutil.relativedelta import relativedelta
 from django import template
 from django.db import transaction
 from django.db.models.signals import post_delete, post_save
@@ -27,6 +28,7 @@ from django.urls import reverse
 from django.utils.formats import number_format
 from django.utils.six import text_type
 from django.utils.timesince import timesince
+from django.utils.timezone import now
 
 from eo_gestion.eo_banque.models import LigneBanquePop
 from eo_gestion.eo_facture.models import DELAI_PAIEMENT, Contrat, Facture, Payment
@@ -320,3 +322,33 @@ def payment_post_save(raw, **kwargs):
 @receiver(post_delete, sender=Payment)
 def payment_post_delete(**kwargs):
     transaction.on_commit(impayees.recompute)
+
+
+@register.inclusion_tag('eo_facture/echeances.html')
+def echeances():
+    qs = Contrat.objects.filter(periodicite__isnull=False).prefetch_related('factures')
+
+    until = (now() + relativedelta(months=6)).date()
+    echeances = []
+    for contrat in qs:
+        facture_par_numero_d_echeance = {
+            facture.numero_d_echeance: facture
+            for facture in contrat.factures.all()
+            if facture.echeance and not facture.proforma
+        }
+        for i, periode_debut, periode_fin in contrat.periodicite_echeances(until=until):
+            if i in facture_par_numero_d_echeance:
+                continue
+            echeances.append((periode_debut, periode_fin, i, contrat))
+    echeances.sort(key=lambda x: x[:3])
+    return {
+        'echeances': [
+            {
+                'debut': echeance[0],
+                'fin': echeance[1],
+                'occurrence': echeance[2],
+                'contrat': echeance[3],
+            }
+            for echeance in echeances
+        ],
+    }
diff --git a/eo_gestion/templates/admin/index.html b/eo_gestion/templates/admin/index.html
index 51d57cd..9be5519 100644
--- a/eo_gestion/templates/admin/index.html
+++ b/eo_gestion/templates/admin/index.html
@@ -6,6 +6,7 @@
 
 {% block content %}
 <div id="content-main">
+{% echeances %}
 {% income_by_clients %}
 {% impayees %}
 {% a_facturer %}
diff --git a/setup.py b/setup.py
index 7207f6e..1208594 100644
--- a/setup.py
+++ b/setup.py
@@ -20,6 +20,7 @@ install_requires = [
     'XStatic-Select2',
     'gadjo',
     'django-mellon',
+    'python-dateutil',
 ]
 
 
diff --git a/test-requirements.txt b/test-requirements.txt
index 02215b6..8ce315d 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -6,3 +6,4 @@ pytest-freezegun
 httmock
 django-webtest
 uwsgidecorators
+pyquery
diff --git a/tests/test_admin.py b/tests/test_admin.py
new file mode 100644
index 0000000..85d5c11
--- /dev/null
+++ b/tests/test_admin.py
@@ -0,0 +1,58 @@
+# barbacompta - invoicing for dummies
+# Copyright (C) 2022 Entr'ouvert
+#
+# This program is free software: you can redistribute it and/or modify it
+# under the terms of the GNU Affero General Public License as published
+# by the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import pytest
+
+
+class TestLoggedIn:
+    @pytest.fixture
+    def app(self, app):
+        # login
+        response = app.get('/').follow()
+        response.form['username'] = 'admin'
+        response.form['password'] = 'admin'
+        response.form.submit()
+        return app
+
+    def test_contrat_recurrent_no_debut(self, app):
+        response = app.get('/eo_facture/contrat/add/')
+        response.form['client'].force_value('1')
+        response.form['intitule'] = 'Contrat 1'
+        response.form['periodicite'] = 'annuelle'
+        response = response.form.submit('_continue')
+        assert len(response.pyquery('.errorlist'))
+
+    def test_contrat_recurrent_debut_changed(self, app):
+        response = app.get('/eo_facture/contrat/add/')
+        response.form['client'].force_value('1')
+        response.form['intitule'] = 'Contrat 1'
+        response.form['periodicite'] = 'annuelle'
+        response.form['periodicite_debut'] = '2018-12-01'
+        response = response.form.submit('_continue').follow()
+        response.form['periodicite_debut'] = '2018-12-02'
+        response = response.form.submit('_continue').follow()
+
+        # Créer la facture de première échéance
+        response = app.get('/')
+        assert 'facturer-echeance' in response.form.action
+        response = response.form.submit().follow()
+
+        # Essayons de modifier le début
+        response = response.click('Contrat', index=1)
+        response.form['periodicite_debut'] = '2018-12-01'
+        response = response.form.submit('_continue')
+        # Il y a une erreur
+        assert len(response.pyquery('.errorlist.nonfield'))