Which months have 31 days?

January, March, May, July, August, October and December each have 31 days. That is seven of the twelve months. The remaining four full-length months, April, June, September and November, have 30 days, and February has 28 or 29 depending on whether it is a leap year.

Do all months have at least 28 days?

Yes. Every month in the Gregorian calendar has at least 28 days, because February is the shortest at 28 days in a common year. It is the answer to the old riddle asking how many months have 28 days: all twelve of them do.

How many days are in a year?

A common year has 365 days and a leap year has 366. The extra day is added to February as 29 February, which happens in most years divisible by four. The average length across the Gregorian cycle is 365.2425 days.

Why do July and August both have 31 days?

The two long months sit together because the Julian reform assigned those lengths, not because an emperor stole a day from February. That story appears only in medieval writing. Quintilis was renamed for Julius Caesar and Sextilis for Augustus after their lengths were already set.

Days in Each Month | months.now

Almost every plan runs into the same small obstacle sooner or later: the days in each month are not the same. Seven months are long, four are short, and February is shorter still. That uneven pattern was inherited from Roman practice rather than designed, and it quietly complicates rent schedules, payroll runs, notice periods and anything counted in whole weeks.

This article sets out how many days in each month there are, explains February's two cases, and gives the fastest ways to recall the full set without looking anything up. If you would rather read the answer straight off a screen, the days in month page returns the figure for any month you pick, and this month shows the current one with its length already worked out.

How Many Days in Each Month?

Seven months have 31 days, four have 30, and February has 28 in a common year or 29 in a leap year. The long months are January, March, May, July, August, October and December. The short months are April, June, September and November.

Added together, that comes to 365 days in a common year and 366 in a leap year. No month in the Gregorian calendar has fewer than 28 days or more than 31. Only February in a common year is exactly four weeks long, which is why a monthly cycle and a weekly cycle never quite stay in step.

The Full List, Month by Month

Here is the complete reference in calendar order, with each month's number alongside its length:

January (1): 31 days.
February (2): 28 days, or 29 in a leap year.
March (3): 31 days.
April (4): 30 days.
May (5): 31 days.
June (6): 30 days.
July (7): 31 days.
August (8): 31 days.
September (9): 30 days.
October (10): 31 days.
November (11): 30 days.
December (12): 31 days.

If you work with dates in spreadsheets or software, the month number matters as much as the name, and the month number reference pairs the two so you never have to count on your fingers to find that September is the ninth month.

Read down that list and the shape of the year emerges. The days in each month alternate between 31 and 30 through the first half, break at July and August where two long months sit together, then alternate again in the opposite phase to the end of December. Only February stands outside the pattern entirely. Anyone memorising the days in each month by brute force is really memorising where that break falls, because everything else follows from it.

Why Is February the Odd One Out?

February is short because the early Roman calendar had to absorb its leftover days somewhere, and February was last in the year. The Romans began their year in March, so the final month took the shortfall and kept it ever since.

The ten-month Roman year is traditionally said to have been extended by Numa Pompilius, who added Januarius and Februarius to cover the winter gap. Februarius took its name from februa, the purification rites held during it. When the Julian reform under Julius Caesar fixed the year at 365 days with an extra day every fourth year, that extra day was inserted into February, which is why 29 February exists at all. The leap year rule and the reasons behind it are covered in full in February and leap years.

The Fastest Ways to Recall the Days in Each Month

Three methods cover it: the rhyme, the knuckles, and a single anchor fact. Most people find that one of them sticks permanently and the others never do, so it is worth trying all three rather than forcing the popular one.

All three exist because there is nothing to work out. The days in each month cannot be derived from anything; they can only be recalled, which is why the mnemonics have survived for centuries while far more useful facts have not.

The Rhyme

"Thirty days hath September, April, June, and November. All the rest have thirty-one, except February alone, which has twenty-eight days clear, and twenty-nine in each leap year." The rhyme works by listing only the four short months, leaving everything else at 31 by default. It is compact, but it depends on recalling the list in the right order.

The Knuckles

Make a fist and count across the knuckles and the dips between them. Knuckles are long months, dips are short ones. Because the pattern is physical rather than verbal, it survives under pressure better than the rhyme does. The step-by-step method, including the one-hand and two-hand versions, is set out in the knuckle mnemonic.

One Anchor Fact

If you only remember one thing, remember the four thirty-day months: April, June, September, November. Everything else is 31 except February. Reducing the problem to a four-item list is why this works at all.

Why July and August Both Have 31 Days

July and August sit side by side with 31 days each, which breaks the otherwise tidy alternation. The popular explanation is that Augustus took a day from February so his month would not be shorter than Julius Caesar's. It is a good story and it is almost certainly false, appearing only in medieval writing more than a thousand years later.

The likelier account is simply that the Julian reform distributed the days that way from the start. Quintilis, the fifth month of the old Roman year, was renamed Julius for Julius Caesar; Sextilis, the sixth, was later renamed Augustus for the emperor. Both months already had their lengths before the renaming. That the numbering feels wrong today, with September through December sitting as the ninth to twelfth months despite meaning seventh to tenth, is explained in why September is the ninth month.

Where the Days in Each Month Actually Matter

The uneven month lengths stop being trivia the moment money or deadlines are involved. Four situations account for most of the trouble:

Billing and notice periods: a 30-day notice served in January expires in early March, not on 1 February, because January has 31 days.
Payroll and daily rates: dividing a monthly salary by the days in the month produces a different daily rate in February than in March.
Quarter comparisons: the first calendar quarter has 90 or 91 days while the others have 91 or 92, so quarter-on-quarter revenue is not comparing equal spans. The quarter page shows which quarter a date falls in.
Subscription renewals: a subscription started on the 31st has no matching date in a 30-day month, so systems must roll back to the last day.

Whenever a schedule spans a month boundary, the days in the months involved change the answer. Interest accruing daily, holiday entitlement drawn down monthly and anything measured per day rather than per month all shift with the calendar rather than with the business. Planning ahead is easier when you can see the next block laid out, which is what next month is for.

Conclusion

The days in each month follow a short, learnable pattern: 31 days for January, March, May, July, August, October and December; 30 days for April, June, September and November; and 28 or 29 for February. The lopsidedness is Roman inheritance, preserved through the Julian reform and carried into the Gregorian calendar we still use. Learn the four thirty-day months and the rest falls into place. To check the days in each month for any month at once, open the days in month page, or start from the months.now homepage.

How Many Days in Each Month: The Complete Reference