Seven months have 31 days, four have 30 days, and February has 28 days or 29 in a leap year. The seven long months are January, March, May, July, August, October and December. The four short ones are April, June, September and November. The days-in-month calculator confirms the exact count for any month and year, and handles February’s leap-year change.
The full list
- 31 days: January, March, May, July, August, October, December
- 30 days: April, June, September, November
- 28 or 29 days: February
That covers every month. The only one that changes length is February.
The knuckle trick
A quick way to remember month lengths without a calendar uses your knuckles. Make a fist and start counting months along the top, beginning with January on the first knuckle, February in the dip, March on the next knuckle, and so on. Every knuckle is a 31-day month and every dip is a shorter one. When you reach the last knuckle at July, start again from the first knuckle for August, which keeps the two long months in a row, July and August, correct.
Why February changes
February has 28 days in a common year and 29 in a leap year. The extra day exists because a solar year is about 365.24 days, slightly more than 365. Adding a leap day roughly every four years takes up the slack. A year is a leap year if it divides by 4, except century years, which must also divide by 400. So 2024 gives February 29 days, while 1900 did not. For the full rule, see how to tell if a year is a leap year.
Why the year matters here
Because February changes length, and because the weekday a month starts on depends on the year, the days-in-month calculator asks for both a month and a year. It then returns the correct day count and the weekdays the month begins and ends on, which helps when laying out a calendar or working out a daily rate.