diff --git a/journals/models.py b/journals/models.py
index c8accb008ebe2282920f886fc87b3509a1a38f67..6ec91dd1d16be97571fb592f0becbbabc22563fd 100644
--- a/journals/models.py
+++ b/journals/models.py
@@ -61,7 +61,7 @@ class Journal(models.Model):
         for pub in pubs:
             if pub.citedby and pub.latest_citedby_update:
                 ncites += len(pub.citedby)
-                deltat += (pub.latest_citedby_update - pub.publication_date).seconds
+                deltat += (pub.latest_citedby_update.date() - pub.publication_date).days
         return (ncites * 3600 * 24 * 365.25/deltat)
 
 
@@ -93,8 +93,8 @@ class Volume(models.Model):
         for pub in pubs:
             if pub.citedby and pub.latest_citedby_update:
                 ncites += len(pub.citedby)
-                deltat += (pub.latest_citedby_update - pub.publication_date).seconds
-        return (ncites * 3600 * 24 * 365.25/deltat)
+                deltat += (pub.latest_citedby_update.date() - pub.publication_date).days
+        return (ncites * 365.25/deltat)
 
 
 class Issue(models.Model):
@@ -157,7 +157,7 @@ class Issue(models.Model):
         for pub in pubs:
             if pub.citedby and pub.latest_citedby_update:
                 ncites += len(pub.citedby)
-                deltat += (pub.latest_citedby_update - pub.publication_date).seconds
+                deltat += (pub.latest_citedby_update.date() - pub.publication_date).days
         return (ncites * 3600 * 24 * 365.25/deltat)
 
 
@@ -262,7 +262,7 @@ class Publication(models.Model):
         """
         if self.citedby and self.latest_citedby_update:
             ncites = len(self.citedby)
-            deltat = (self.latest_citedby_update - self.publication_date).seconds
+            deltat = (self.latest_citedby_update.date() - self.publication_date).days
             return (ncites * 3600 * 24 * 365.25/deltat)
         else:
             return 0