Leap Year Checker
Check whether a year is a leap year, with the rule that governs it explained.
Does this year have a leap day
A leap year has an extra day, the 29th of February, added to keep the calendar aligned with Earth's orbit. This checks whether any year is a leap year, and understanding why involves a rule more subtle than most people realise.
The rule is not just every four years
Most people know leap years come every four years, but that is only part of the rule, and the exceptions are what keep the calendar accurate over centuries:
| Rule | Result |
|---|---|
| Divisible by 4 | Leap year... |
| ...but divisible by 100 | ...not a leap year... |
| ...but divisible by 400 | ...leap year after all |
So 2000 was a leap year (divisible by 400), but 1900 was not (divisible by 100 but not 400), even though both are divisible by four. This is why the simple every-four-years belief occasionally gives the wrong answer around century years.
Why the rule is so fiddly
The complication exists because a year is not exactly 365 and a quarter days long — it is very slightly less. Adding a leap day every four years overcorrects by a tiny amount, which would slowly drift the calendar over centuries, so the century rules remove three leap days every four hundred years to compensate almost perfectly. It is a beautiful bit of calendar engineering that keeps our dates aligned with the seasons over thousands of years. The extra day lands on the 29th of February, which is why people born on that date have a birthday only in leap years, a quirk that makes the leap day a small curiosity as well as a practical necessity.
Questions & answers
What is the leap year rule?
A year is a leap year if divisible by four, except century years, which must be divisible by 400 — so 2000 was a leap year but 1900 was not.
Why isn't it simply every four years?
Because a year is slightly less than 365 and a quarter days, so adding a day every four years overcorrects; the century rules remove a few to keep the calendar accurate.
Why does the leap day fall on 29 February?
February is the short month, so the extra day is appended there — which is why people born on the 29th have a birthday only in leap years.
Is anything uploaded?
No. The check happens in your browser.