diff --git a/chainladder/core/base.py b/chainladder/core/base.py
index 9d8c3109..51648611 100644
--- a/chainladder/core/base.py
+++ b/chainladder/core/base.py
@@ -258,7 +258,7 @@ def _to_datetime(data, fields, period_end=False, format=None):
     def _development_lag(origin, valuation):
         """For tabular format, this will convert the origin/valuation
         difference to a development lag"""
-        return ((valuation - origin) / (365.25/12)).round('1d').dt.days
+        return ((valuation - origin) / (365.25/12)).dt.round('1d').dt.days
 
 
     @staticmethod