I've seen a few people singing the praises of the Thirty Days Hath September rhyme, but I've always been a bigger fan of the knuckle trick. If you don't know how the knuckle trick works, it goes like this: Count the months on your knuckles and the grooves between your knuckles. When you run out of knuckles on one hand, move to the other. Leave out your thumb knuckle. Every month that lands on a knuckle is 31 days, every month that lands on a groove between knuckles is 30 days (or 28 for February).

As an added bonus, it takes slightly less than fifteen minutes to figure out how many days are in November using this method. Progress, thy name is Erik!