Today is the first of five Mondays this month. It’s unusual enough to have five anything in February; it happens only in a leap year.

I found myself wondering when was the last time we had a February with five Mondays, and when will be the next.

The answer to the question is the same as answer to this question: when was the last time a leap year began on a Friday? and when’s the next?

There are, of course, only fourteen calendars, and they’re easy to find or compute. What’s a little more toilsome is knowing way out of sequence which one to use for a given year.

Given the year, you can find the right calendar on timeanddate.com; but that’s not the answer to this question. Do you know how to figure it out?