Leap Year Checker Calculators
Check whether a year is a leap year, and find the next few.
Leap Year Checker is a free online tool that check whether a year is a leap year, and find the next few. It runs entirely in your web browser using plain JavaScript, so files are processed on your own device and never uploaded to a server. There is no sign-up, no file size limit imposed by the site, no watermark and no paid tier.
- Price
- Free — no account, no quota, no watermark
- Category
- Calculators
- Where it runs
- In your browser, on your device
- Files uploaded
- None
- Technology
- plain JavaScript
- Settings
- 1
- Works offline
- Yes, after the first visit
About Leap Year Checker
The rule is divisible by 4, except centuries, unless divisible by 400. That third clause exists because the tropical year is 365.2422 days rather than 365.25 — the Julian calendar's simpler rule drifted by about three days every four centuries, which is why 1582 lost ten days overnight when the Gregorian calendar arrived.
How to use it
- Enter year.
- Results update the moment anything changes.
The one setting
| Setting | What it does | Default |
|---|---|---|
| Year | Range 1–9999. | 2026 |
Under the hood
| Runs on | plain JavaScript — runs the whole thing |
| Controls | Year |
Questions
Was 2000 a leap year?
Yes — divisible by 400, so the century exception was itself excepted. 1900 was not, and 2100 will not be. A great many programs written before 2000 got this wrong.
What are the limits on year?
It accepts 1 to 9999, starting at 2026.
Is the arithmetic exact?
It uses double-precision floating point — about 15 significant figures, far more than the inputs justify. Displayed rounding is cosmetic; the underlying numbers are not rounded between steps, so chained results do not drift.