diff --git a/src/calibre/utils/formatter_functions.py b/src/calibre/utils/formatter_functions.py
index 63264e6379..55bad6c7e8 100644
--- a/src/calibre/utils/formatter_functions.py
+++ b/src/calibre/utils/formatter_functions.py
@@ -785,7 +785,7 @@ class BuiltinDaysBetween(BuiltinFormatterFunction):
         except:
             return ''
         i = d1 - d2
-        return str(i.days)
+        return str('%d.%d'%(i.days, i.seconds/8640))
 
 
 builtin_add         = BuiltinAdd()