How Many Days Are in Each Month?
The months are an uneven set: seven have 31 days, four have 30, and February has either 28 or 29. There is no simple pattern, which is exactly why so many memory tricks exist — and why adding "one month" to a date is rarely the same number of days twice.
The length of every month
Here is the full list:
- January — 31 days
- February — 28 days (29 in a leap year)
- March — 31 days
- April — 30 days
- May — 31 days
- June — 30 days
- July — 31 days
- August — 31 days
- September — 30 days
- October — 31 days
- November — 30 days
- December — 31 days
Two ways to remember them
The knuckle trick: make a fist and count across the knuckles and dips. Each raised knuckle is a 31-day month and each dip between them is a shorter month; run out at July and start again at the first knuckle for August. The rhyme works too: "Thirty days hath September, April, June, and November; all the rest have thirty-one, except February." The Days in Each Month tool shows them all at a glance.
Why February is the odd one out
February is short for historical reasons rooted in the old Roman calendar, and it is the month that carries the calendar's correction: the leap day. In a leap year it gains a 29th day so the year totals 366 — see what is a leap year for the rule, or check any year with the Leap Year Calculator.
Why month lengths matter for date math
Because months vary, "one month later" is not a fixed number of days. Good date tools clamp to the month end — 31 January plus one month lands on 28 February (or the 29th in a leap year), because there is no 31 February. When you shift a date by days rather than months, the Add Days to Date calculator counts real calendar days so month lengths are handled automatically.