Leap Year Checker
Is any year a leap year? The full rule, explained, with the next five.
About this checker
Type a year; get the verdict with the exact rule that decided it — including the century wrinkle most people half-remember — and the next five leap years for planning.
The rule, and why it exists
Every 4th year leaps, EXCEPT century years, EXCEPT-except centuries divisible by 400: so 2024 leaps, 1900 didn't, 2000 did. The reason is a mismatch of about 11 minutes: the solar year runs 365.2422 days, and plain +1-every-4 (Julius Caesar's system) overshoots enough to drift the calendar a day every 128 years — by 1582 the equinox had wandered 10 days and Pope Gregory's reform cut the century leaps to fix it, deleting 10 October days outright that year. The Gregorian average of 365.2425 days is off by one day in ~3,200 years, which posterity can patch. The famous software version of the wrinkle: Excel believes 1900 was a leap year (a bug kept for Lotus 1-2-3 compatibility, forever). February 29 birthdays age legally on March 1 in most places — the age calculator handles them properly, and day of the week knows what weekday any Feb 29 fell on.
Frequently asked questions
Is 2100 a leap year?
No — it's divisible by 100 but not 400, so it skips. The next century year to leap is 2400. (2000 leaped for the same 400 rule.)
Why do century years skip the leap?
Because +1 day every 4 years slightly overshoots the true solar year (365.2422 days). Dropping three leap days every 400 years brings the average to 365.2425 — close enough to drift only a day in 3,200 years.
When do February 29 babies celebrate?
In common years, most jurisdictions age them legally on March 1; culturally it's celebrant's choice between Feb 28 and Mar 1. True birthdays come every 4 years — with the century exception.
Why does Excel think 1900 was a leap year?
A deliberate bug inherited from Lotus 1-2-3 for file compatibility, then kept forever. Date arithmetic crossing February 1900 in spreadsheets is off by one — a real gotcha in historical data.