Remember this rhyme?
Thirty days hath September,
April, June, and November,
all the rest have thirty-one.
Excepting February alone
Which has but twenty-eight days clear,
And twenty-nine in each Leap Year.
Use your Knuckles!
Make a fist.
If the month is on a knuckle, it has 31 days. Otherwise is has 30 or less days.
Starting with the 1st knuckle as January,
The space between knuckles as February,
2nd Knuckle is March… etc.
Once you get to the fourth knuckle, July, start over at the first knuckle for August.