Leap Year Calculator
Type any year and find out instantly whether it is a leap year, how many days it has, and the nearest leap years before and after. Uses the full Gregorian rule, including the century exceptions that trip people up (1900 was not a leap year; 2000 was).
Example: with Year 2024 → Verdict: 2024 is a leap year - February 2024 has 29 days. 2024 is divisible by 4 (and not a century year)..
- Days in that year366 days
- Next leap years2028, 2032, 2036
- Previous leap year2020
Computed by the calculator below using its default values. Change any input to see your own numbers.
Gregorian rule: every 4th year leaps, except centuries - unless divisible by 400. That trims the average year to 365.2425 days, within 27 seconds of the solar year.
The rule and why it exists
A calendar year is 365 days, but Earth's trip around the Sun takes about 365.2422 days. Julius Caesar's fix - add a day every 4th year - overshoots, averaging 365.25. By 1582 the calendar had drifted 10 days against the seasons, so the Gregorian reform added the century exception: century years leap only when divisible by 400. That yields 97 leap years per 400 and an average year of 365.2425 days, accurate to about one day in 3,200 years.
So 1900, 2100, 2200, and 2300 are common years, while 1600, 2000, and 2400 leap. Everyone alive through February 2000 experienced the rare divisible-by-400 exception - which is partly why many people never notice the century rule at all.
Where leap years bite
Leap years matter beyond February 29 birthdays: interest calculations on actual/365 versus actual/actual day-count conventions, annualizing daily rates, payroll years with 366 days, and any spreadsheet that assumes years times 365. A 30-year mortgage span contains 7 or 8 leap days, and date-difference math that ignores them drifts by a week.
How it’s calculated
Leap test: year divisible by 4 AND not by 100, OR divisible by 400 - the Gregorian calendar rule in force since 1582 (adopted 1752 in the British colonies). Days in year = 366 if leap, else 365. Next/previous leap years scan the same rule. For years before the Gregorian adoption the rule is applied proleptically - historical dates before 1582 actually followed the Julian every-4th-year rule.
Years are treated as Gregorian throughout; pre-1582 (or pre-1752 British) historical documents used the Julian calendar, where every 4th year leaped including centuries.
The rule applied to tricky years
| Year | Rule that decides | Leap? |
|---|---|---|
| 1900 | Century, not divisible by 400 | No - 365 days |
| 2000 | Divisible by 400 | Yes - 366 days |
| 2024 | Divisible by 4, not a century | Yes - 366 days |
| 2026 | Not divisible by 4 | No - 365 days |
| 2100 | Century, not divisible by 400 | No - 365 days |
Gregorian calendar rules (papal bull Inter gravissimas, 1582); modern civil calendar per NIST.
Common mistakes
- Testing only divisibility by 4 - that wrongly makes 1900 and 2100 leap years; the century exception is the whole point of the Gregorian reform.
- Assuming 2000 was a common year by over-applying the century rule - divisible by 400 restores the leap day.
- Using year length 365.25 in financial or astronomical math when the calendar average is 365.2425 and the true solar year is 365.2422.
- Applying the Gregorian rule to historical dates before 1582 (or 1752 in Britain/colonies), when the Julian rule was in force.
Frequently asked questions
What is the leap year rule?
A year is a leap year if it is divisible by 4 and not by 100, or if it is divisible by 400. So 2024 and 2000 leap; 1900, 2026, and 2100 do not.
Why was 1900 not a leap year but 2000 was?
Both are century years, and centuries skip the leap day unless divisible by 400. 1900 / 400 = 4.75, so it stayed at 365 days; 2000 / 400 = 5 exactly, so February 29, 2000 existed.
Why do we need leap years at all?
The solar year is about 365.2422 days. Without added days the calendar would slide roughly one day every four years - after a few centuries July would land in winter. One extra day every four years, minus three per 400, keeps the drift to about a day in 3,200 years.
How many leap years are there in a century?
Usually 24 or 25. A 100-year span holds 25 multiples of 4, but loses one when its century year (like 1900 or 2100) fails the 400 test - the 1901-2000 span kept all 25 because of the year 2000.
When is the next leap year?
From 2026, the next leap years are 2028, 2032, and 2036 - every four years without interruption until 2100, the next skipped century.