diff --git a/plasim/src/calmod.f90 b/plasim/src/calmod.f90
index 0d143ea78c8260a93de1ea4021edcafa82f04ecf..26016a2960a9ff5caace71ad3f8c665d45ba977d 100644
--- a/plasim/src/calmod.f90
+++ b/plasim/src/calmod.f90
@@ -72,6 +72,7 @@
       else
          kmon = (kyday-1) / n_days_per_month
          kday = kyday - n_days_per_month * kmon
+         kmon = kmon+1
       endif
       return
       end