Why is February shorter than every other month?

It's a leftover from the Roman calendar, where winter months were added last and February ended up with the spare days. Later reforms never fixed it.

How often does February have 29 days?

Roughly every four years: specifically, years divisible by 4, minus the century years that aren't divisible by 400.

Was 2000 a leap year?

Yes. It's divisible by 400, so it kept its 29 February. 1900 and 2100 don't, since they're divisible by 100 but not 400.

Does the Persian calendar have a 29 February?

No. Its leap day is 30 Esfand, the extra day at the end of the Persian year.

Calendar history تاریخ تقویم

Why does February have 28 days (and sometimes 29)?

July 1, 2026 ۱ July ۲۰۲۶ · 2 min read · ۲ دقیقه مطالعه

On this pageدر این صفحه

Every other month is 30 or 31 days. February sits there at 28, the odd one out, and the reason is basically two thousand years of accumulated calendar politics.

Blame the Romans

The earliest Roman calendar had ten months and just ignored winter. Those roughly 60 cold days between the end of one year and the start of the next weren’t assigned to any month at all. Winter didn’t matter for the farming calendar, so nobody bothered.

When January and February eventually got added to fill that gap, February ended up last in the year and got the leftover days (source: Encyclopædia Britannica, “Julian calendar”). Romans also had a thing about even numbers being unlucky, so months were mostly given 29 or 31 days. February took the hit as the one even-numbered, short month, partly because it held a festival of purification and ritual, so a shorter month was tolerable there.

Later reshuffles (the Julian reform, then a few imperial ego-driven tweaks to month lengths) locked the pattern in. By the time the dust settled, February was stuck at 28.

The 29th day, and the rule behind it

A solar year is about 365.2422 days, not a whole number. Those leftover quarter-days add up, so the calendar wedges in an extra day every so often to stop the seasons from drifting. For example, four years of that leftover quarter-day add up to roughly one whole day, which is the day 29 February restores. That extra day gets tacked onto February: 29 February, the leap day.

The Gregorian rule is:

Divisible by 4 → leap year (so 29 February exists)
…unless divisible by 100 → not a leap year
…unless divisible by 400 → leap year after all

That’s why 2000 was a leap year but 1900 wasn’t. Check any year:

Is a given year a leap year? آیا یک سال مشخص کبیسه است؟

The Persian calendar does it differently

Since this site lives in two calendars, it’s worth a look. The Persian (Jalali) calendar also adds a leap day, but it lands on 30 Esfand (the last month), not February, and it follows a 33-year cycle rather than the 4/100/400 rule. I dug into the cycle in Persian leap years, explained, and into that curious leap day in 30 Esfand explained. The motivation is the same, keeping the calendar synced to the Sun, but the bookkeeping is its own thing.

If you’ve got a date near the end of February or Esfand and need to move it between calendars, the converter handles the leap-day edge cases so you don’t have to think about them.

Why is February shorter than every other month?
It's a leftover from the Roman calendar, where winter months were added last and February ended up with the spare days. Later reforms never fixed it.
How often does February have 29 days?
Roughly every four years: specifically, years divisible by 4, minus the century years that aren't divisible by 400.
Was 2000 a leap year?
Yes. It's divisible by 400, so it kept its 29 February. 1900 and 2100 don't, since they're divisible by 100 but not 400.
Does the Persian calendar have a 29 February?
No. Its leap day is 30 Esfand, the extra day at the end of the Persian year.

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