diff --git a/app/models/property.rb b/app/models/property.rb
index 103ae9d..e6a684c 100644
--- a/app/models/property.rb
+++ b/app/models/property.rb
@@ -114,7 +114,7 @@ class Property
             diff_month = diff_month + 12 if diff_month < 0
             e_month = stime_tp.month + diff_month
             e_year = stime_tp.year + (booking.end_time.year-booking.start_time.year)
-            e_month = e_month - 12
+            e_month = e_month - 12 if e_month >12
             b_sdata = Time.local(stime_tp.year,stime_tp.month,booking.start_time.day,booking.start_time.hour,booking.start_time.minute).to_datetime
             b_edata = Time.local(e_year,e_month,booking.end_time.day,booking.end_time.hour,booking.end_time.minute).to_datetime
           elsif b_interval == 'week'