Leap Year Calculator
Is it a leap year? The divisible-by-4, -100 and -400 test worked through for any year, the next leap years, and what weekday 29 February falls on.
Leap Year Calculator: with the default inputs, leap year? is No — 2026 is a common year.
Any year on the Gregorian calendar. Century years are the interesting ones.
- Why
- 2026 is not divisible by 4, so it is a common year.
- Days in the year
- 365
- Weeks in the year
- 52 weeks and 1 day
- 29 February falls on
- there is no 29 February this year
- Next leap year
- 2028
- Previous leap year
- 2024
- Years until the next one
- 2
Assumptions
- The Gregorian rule is applied to every year, including those before the calendar's adoption in 1582 (the proleptic Gregorian calendar).
- The tropical year is taken as 365.2422 days, the mean over the current era; it changes slightly over millennia.
- No correction is applied for the residual drift of roughly one day per 3,200 years, because none has been adopted.
| Year | 29 February falls on | Years after the one before |
|---|---|---|
| 2028 | Tuesday | 4 |
| 2032 | Sunday | 4 |
| 2036 | Friday | 4 |
| 2040 | Wednesday | 4 |
| 2044 | Monday | 4 |
| 2048 | Saturday | 4 |
| Rule | Average year length | Drift against the seasons |
|---|---|---|
| No leap years at all | 365 days | about 1 day every 4 years |
| Every 4th year (Julian) | 365.25 days | about 1 day every 128 years |
| …except century years | 365.24 days | about 1 day every 240 years, the other way |
| …unless divisible by 400 (Gregorian) | 365.2425 days | about 1 day every 3,200 years |
The tropical year is about 365.2422 days. Each rule is a correction to the one above it, and together they leave an error of roughly one day in 3,200 years.
How this is worked out
The formula
A year is a leap year when: it is divisible by 4, and NOT divisible by 100, unless it is also divisible by 400. So 2024 is (divisible by 4, not a century year), 1900 is not (century, not divisible by 400), and 2000 is (century, but divisible by 400). Over 400 years that gives 97 leap days, an average year of 365.2425 days.
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Year
- Any year on the Gregorian calendar. Century years are the interesting ones.from 1 to 9999 · whole numbers only · defaults to 2026
What you get back
- Leap year?main answer
- Why
- Days in the year
- Weeks in the year
- 29 February falls on
- Next leap year
- Previous leap year
- Years until the next one
What this assumes
- The Gregorian rule is applied to every year, including those before the calendar's adoption in 1582 (the proleptic Gregorian calendar).
- The tropical year is taken as 365.2422 days, the mean over the current era; it changes slightly over millennia.
- No correction is applied for the residual drift of roughly one day per 3,200 years, because none has been adopted.
About this calculator
A year on the calendar has to keep pace with a year in the sky, and the two do not divide evenly. The Earth takes about 365.2422 days to go round the Sun, so a 365-day calendar slips almost a quarter of a day every year — a month out of step every 120 years, which is how Easter ends up in the wrong season.
The rule, and why it has three parts
Each part of the leap-year rule is a correction to the one before it:
- Divisible by 4 adds a day every fourth year, making the average year 365.25 days. That overshoots, because the real figure is 365.2422.
- Except century years removes three leap days per 400 years, bringing the average to 365.24. Now it undershoots.
- Unless divisible by 400 puts one of them back, landing on 365.2425 days — within half a minute a year of the truth.
That is why 1900 had no 29 February and 2000 did. Most people alive today have never seen a skipped leap year, which is exactly why the 1900 case surprises them: the next one is 2100.
What it is actually used for
Leap years are not trivia if you write software or run payroll. A leap year has 366 days, which means:
- Daily interest, per-diem rates and SaaS proration all change by 1/365th.
- A "year" of 52 weeks is 364 days, so an annual salary divided by 52 is not an annual salary.
- Anything storing a birthday of 29 February needs a documented answer for what happens in the other three years — the law differs by country, and most systems quietly pick 1 March or 28 February without saying so.
The part the rule still gets wrong
365.2425 against 365.2422 leaves roughly one day of drift every 3,200 years, and the tropical year is itself slowly shortening. There is no adopted rule for fixing it, because nobody needs to decide for another millennium. Proposals exist — dropping a leap day every 3,200 years is the usual one — but none is official, so this calculator applies the Gregorian rule indefinitely.
Frequently asked questions
▸Is 2100 a leap year?
No. It is divisible by 4, but it is a century year and 2100 is not divisible by 400, so the leap day is skipped. It will be the first skipped leap year since 1900, and the first one almost anyone alive has seen.
▸Why was 2000 a leap year but 1900 not?
Both are century years, so both are candidates for being skipped — but 2000 is divisible by 400 and 1900 is not. The 400-year exception exists because skipping every century year would over-correct and push the calendar the other way.
▸How many leap years are there in 400 years?
Ninety-seven. A hundred years are divisible by 4, three of the four century years in the cycle are skipped, giving 97 leap days per 400 years and an average year of 365.2425 days.
▸What happens to a 29 February birthday in other years?
It depends where you are. Most systems and most jurisdictions treat the legal anniversary as 1 March, but some use 28 February, and a good many pieces of software never decide and behave differently in different places. If you are building something, pick one and write it down.
▸Does the leap-year rule ever get it wrong?
Slowly. 365.2425 days against a real 365.2422 leaves about one day of drift every 3,200 years. No correction has been adopted, and the usual proposal — skipping a leap day once every 3,200 years — remains a suggestion rather than a rule.
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