Number of odd days in a non-Leap year = 1. Numbe of odd days in a Leap year = 2. Two year have same calender when number of odd days between two years is 7. Between 2009 and 2015: Number of non-leap year = 5 = 5 odd days Number of Leap year = 1 = 2 odd days Hence, 2015 have same calendar as 2009.