Leap Year Calculator
The four-year hiccup — which years leap, why centuries need dividing by 400, and when the next 29th of February lands.
Leap Year Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Gregorian rule only — no Julian or historical calendar reforms
- Years 1900 to 2100
In short: 2026 is not a leap year — 365 days — and the next one is 2028, whose 29th of February falls on a Tuesday, then 2032, 2036 and 2040. The rule is divisible by four, EXCEPT centuries, which must divide by 400: 2000 leapt, 1900 did not, 2100 will not. That extra quarter-day per year is why the whole apparatus exists — the calendar refuses to drift out of the seasons.
Formula
leap = divisible by 4, except centuries, which must divide by 400
The tropical year runs about 365.2422 days, so every fourth year gets a 366th day — and the three dropped century leap-days per four hundred years keep the average at 365.2425. The rule names both halves: divisible by four, except century years, which leap only when divisible by 400. 2000 divided by 400 and leapt; 1900 divided by 100 alone and did not; 2100 will follow 1900.
Worked Example
- Enter the year.
- Read the verdict and the rule that decided it.
- Check the next and previous leap years.
Defaults: 2026 — not a leap year; next 2028 (29 February on a Tuesday), then 2032, 2036, 2040; previous 2024.
Strengths & Limits Of This Model
Where this engine is strong
- The century rule named with its examples
- Next-and-previous walked, weekday included
Where it stops
- One year per run
Practical Use Cases
Date checks
does February 29 exist this year
Anniversaries
which birthdays clamp and when
Curiosity
the century rule, settled
Methodology & Editorial Standards
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Leap Year Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
Why does the calendar need leap years?
A year is about 365.2422 days — the quarter day left over compounds. Leap days hold the calendar against the seasons; without them the months would drift a day every few years and the solstices would wander.
Why do century years mostly fail?
Because 365.25 — the four-year fix — slightly overshoots. Dropping three century leap-days every four hundred years lands the average on 365.2425, close enough that the error takes millennia to matter. 2100 is the next dropped one.
Was 2000 a leap year?
Yes — the famous exception that proves the rule: divisible by 400, so it leapt despite being a century. 1900, divisible by 100 but not 400, did not; 2400 will.
When does 29 February next land?
The card prints the next leap year and the weekday its 29th falls on — 2028's lands on a Tuesday. Weekdays drift by one per common year and two per leap year, which is exactly the hiccup the extra day buys.
What happens to Feb-29 birthdays?
They clamp to 28 February in common years on this site's convention — the birthday, age and school-age pages all walk the same clamp, so every page agrees on when a leap-day child turns a year.
Which years in my range leap?
The rule is fully mechanical: every fourth year except three in four hundred. From any year the next-and-previous card walks it for you; the pattern never breaks — that is the point of a rule this old.
Is 2100 really not a leap year?
Correct — 2100 divides by 100 but not 400, so it is a common 365-day year despite being a century's turn. Software that forgets this is the y2100 bug waiting to happen.
How precise is the Gregorian fix?
365.2425 against the true 365.2422 — about 26 seconds a year of residual drift, roughly a day in three thousand years. The leap rule is not perfect; it is the best short rule anyone has agreed on.