Leap Year Calculator
Is a year a leap year? Enter any year to test it against the complete Gregorian rules — including the century exception that catches almost everyone — plus the nearest leap years around it.
How to use this calculator
- Enter any year — past or future.
- Press Check to see the verdict and exactly which rule decided it.
- Try 1900 and 2000 to see the century exception in action.
Formula used
So 2024 and 2028 are leap years; 1900 was not (÷100 but not ÷400); 2000 was (÷400). The rule exists because a year is ~365.2425 days: +1 day every 4 years overshoots slightly, and the century corrections trim it back.
Example calculation
2026: not divisible by 4 → not a leap year. Next one: 2028.
1900 vs 2000: both centuries, but 1900 ÷ 400 leaves a remainder (no leap day) while 2000 ÷ 400 = 5 exactly (leap day). This single distinction broke a surprising amount of old software.
Why leap years exist
Earth's orbit takes about 365.2425 days, so a fixed 365-day calendar drifts a full day every four years — left alone, the seasons would slide through the calendar, with July snow in a few millennia. Adding February 29 every fourth year overcorrects slightly (that assumes 365.25), so the Gregorian reform of 1582 removed leap days from most century years, keeping only those divisible by 400.
The result is accurate to about one day in 3,200 years. The system's edge cases are real: people born on Feb 29 legally age on Feb 28 or Mar 1 depending on jurisdiction, and the 1900/2000 asymmetry has bitten spreadsheet and banking software alike.
Why use this calculator?
- Get the century rule right — the part of the leap rule most people forget.
- See the reasoning, not just the verdict, so you can apply the rule yourself.
- Find the nearest leap years for planning Feb 29 birthdays and anniversaries.
Frequently asked questions
Is 2100 a leap year?
No. 2100 is divisible by 100 but not by 400, so it skips the leap day — the first century skip since 1900. Anyone alive then will watch a lot of software get patched.
When do February 29 babies celebrate?
Legally it varies: many jurisdictions treat March 1 as the birthday in common years, others February 28. Socially, most "leaplings" pick one and enjoy having a true birthday only every four years.
Why not just make years exactly 365.25 days?
Because the real year is 365.2425 days — 11 minutes shorter. Pure every-4-years leaping (the old Julian calendar) drifted 3 days per 400 years, which by 1582 had shifted the calendar 10 days off the seasons, forcing the Gregorian correction.