diff --git a/django_lostplaces/lostplaces/admin.py b/django_lostplaces/lostplaces/admin.py
index d56db16..977bc23 100644
--- a/django_lostplaces/lostplaces/admin.py
+++ b/django_lostplaces/lostplaces/admin.py
@@ -17,6 +17,11 @@ class VoucherAdmin(admin.ModelAdmin):
     readonly_fields = ['created_when']
     list_display = ('__str__', 'code', 'created_when', 'expires_when', 'valid')
 
+    def valid(self, instance):
+        return timezone.now() <= instance.expires_when
+    
+    valid.boolean = True
+
 class PhotoAlbumsAdmin(admin.ModelAdmin):
     list_display = ('label', 'place', 'url' )