If you don’t have a calendar on hand, here’s an easy way to figure out which months have 31 days and which have 30:
- Count the months on your knuckles and the grooves between your knuckles. 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).
Starting with your forefinger’s  knuckle:
1st knuckle: Jan (31 days)
Groove: Feb (28 or 30 days)
2nd knuckle: March (31 days)
Groove: April (30 days)
3rd Knuckle: May (31 days)
Groove: June (30 days)
4th Knuckle: July (31 days)
Returning to first knuckle (the forefinger, remember–skip the thumb knuckle)
1st Knuckle: August (31 days)
Groove: September (30 days)
2nd Knuckle: October (31 days)
Groove: November (30 days)
3rd Knuckle: December (31 days)
Instead of moving right to left by starting with your forefinger, you could also start with your pinkie’s knuckle and move left to right. Still works out the same.