Days in Month?

I have [Report Month] = [1,2,3,4,5,6,7,8,9,10,11,12] & [Report Year] = [2011,2012,2013,2014,2016} as separate fields.

How do I calculate number of days in a month for a given year?

For e.g for 2016 Month Feb, Number of days = 29

Need a variable calculation formula?