diff --git a/kfet/statistic.py b/kfet/statistic.py
index 9125e760..e3c89a6d 100644
--- a/kfet/statistic.py
+++ b/kfet/statistic.py
@@ -55,7 +55,7 @@ def lastmonths(nb):
     this_year = first_month_day.year
     this_month = first_month_day.month
     for i in range(1, nb+1):
-        month = this_month - (nb - i) % 12
+        month = ((this_month - 1  - (nb - i)) % 12) + 1
         year = this_year + (nb - i) // 12
         first_days[i] = timezone.datetime(year=year,
                                           month=month,