diff --git a/jdav_web/jdav_web/settings/local.py b/jdav_web/jdav_web/settings/local.py
index 8cc0c79..6aa0129 100644
--- a/jdav_web/jdav_web/settings/local.py
+++ b/jdav_web/jdav_web/settings/local.py
@@ -17,6 +17,7 @@ ECHO_PASSWORD_BIRTHDATE_FORMAT = '%d.%m.%Y'
 # misc
 
 CONGRATULATE_MEMBERS_MAX = 10
+MAX_AGE_GOOD_CONDUCT_CERTIFICATE_MONTHS = 24
 
 # finance
 
diff --git a/jdav_web/members/admin.py b/jdav_web/members/admin.py
index fce409f..20ca616 100644
--- a/jdav_web/members/admin.py
+++ b/jdav_web/members/admin.py
@@ -193,7 +193,7 @@ class MemberAdmin(CommonAdminMixin, admin.ModelAdmin):
          {
              'fields': [
                  ('good_conduct_certificate_presented_date',
-                  'good_conduct_certificate_presentation_needed'),
+                  'good_conduct_certificate_valid'),
                  'has_key', 'has_free_ticket_gym']
          }
         ),
@@ -203,7 +203,7 @@ class MemberAdmin(CommonAdminMixin, admin.ModelAdmin):
     search_fields = ('prename', 'lastname', 'email')
     list_filter = ('group', 'gets_newsletter', RegistrationFilter, 'active')
     list_display_links = None
-    readonly_fields = ['echoed']
+    readonly_fields = ['echoed', 'good_conduct_certificate_valid']
     inlines = [EmergencyContactInline, TrainingOnMemberInline, PermissionOnMemberInline]
     #formfield_overrides = {
     #    ManyToManyField: {'widget': forms.CheckboxSelectMultiple},
diff --git a/jdav_web/members/models.py b/jdav_web/members/models.py
index 48077ee..e971cc9 100644
--- a/jdav_web/members/models.py
+++ b/jdav_web/members/models.py
@@ -279,6 +279,15 @@ class Member(Person):
         else:
             return "{0}, {1}".format(self.street, self.place)
 
+    def good_conduct_certificate_valid(self):
+        """Returns if a good conduct certificate is still valid, depending on the last presentation."""
+        if not self.good_conduct_certificate_presented_date:
+            return False
+        delta = datetime.now().date() - self.good_conduct_certificate_presented_date
+        return delta.days // 30 <= settings.MAX_AGE_GOOD_CONDUCT_CERTIFICATE_MONTHS
+    good_conduct_certificate_valid.boolean = True
+    good_conduct_certificate_valid.short_description = _('Good conduct certificate valid')
+
     def generate_key(self):
         self.unsubscribe_key = uuid.uuid4().hex
         self.unsubscribe_expire = timezone.now() + timezone.timedelta(days=1)