For calculating interest. Anything that's calculated as 30/365, for example, accumulates interest every day, except for the 31st of a month. I'd like to figure out a way to tell how often the 31st has occurred between two dates - for example, between March 15th 2017 and today, there have been 2 31st's - March 31 and May 31st. Is there a good way to figure this out in Excel besides listing out each month in the formula?