Check if a year is a leap year and list upcoming leap years.
Tip: use samples, upload, copy, download, and send-to actions inside the workspace where available.
Leap Year Checker is a free, browser-based tool that helps you get the job done quickly. Check if a year is a leap year and list upcoming leap years. It's built for speed and privacy: Everything runs locally in your browser — your data is never uploaded to a server. No sign-up, no installs, and no daily limits.
Use this tool as the focused step in a larger browser-based workflow.
Review the preview, copy or download the result, and keep everything local in your browser.
Date Calculator: Add or subtract days, weeks, months, or years from a date.
Open toolDate Difference: Difference between two dates in years, months, days, and weeks.
Open toolBoth rules agree about 2026. For dates in this year the Julian calendar runs 13 days behind the Gregorian one.
| Measure | Value |
|---|---|
| Share of years that are leap years | 25.490% |
| Long-run Gregorian average (97 in 400) | 24.250% |
| Expected count over 51 years | 12.37 |
| Julian rule would give (1 in 4) | 13 |
A tropical year is about 365.2422 days. Adding a day every four years overshoots slightly — the Julian average of 365.25 is 11 minutes too long, which had pushed the spring equinox ten days out of place by the 1580s.
The Gregorian fix drops three leap days every 400 years by skipping century years not divisible by 400. That gives 97 leap years per 400, an average of 365.2425 days — accurate to about one day in 3,200 years.
The bug this catches. Code that tests only year % 4 === 0 was correct for every year from 1901 to 2099, so it shipped everywhere and survived. It was wrong in 1900 and will be wrong again in 2100 — and it was famously wrong in Excel, which still treats 1900 as a leap year for compatibility with a 1980s spreadsheet.
