Check Leap Year

A year is a leap year if it is evenly divisible by 4. If it is also divisible by 100, it must be divisible by 400 as well – otherwise the century year is common. So 1900 was common, but 2000 was a leap year.

A calendar year with 366 days instead of 365, achieved by adding February 29. The extra day keeps our calendar aligned with Earth’s 365.2422-day solar orbit.

No. The check runs entirely in your browser – a few integer modulos plus a loop scan for the neighbours. Nothing is sent to any server.

Both are divisible by 100 so both are century years. Only 2000 is also divisible by 400 (2000 ÷ 400 = 5). 1900 ÷ 400 = 4.75, so it failed the extra rule.

Three yes-no rows – divisible by 4, by 100, and by 400 – so you can trace exactly which branch of the rule determined the verdict.

97 times every 400 years in the Gregorian calendar. Nominally every four years, but three out of every four century years (1700, 1800, 1900, 2100, 2200, 2300) are skipped.

For scheduling February 29 events or checking contract anniversaries. The tool scans up to the 999,999-year cap in each direction.

The tool always applies the Gregorian rule. The Julian calendar (every 4 years with no exceptions) was in use before October 1582 in Catholic countries and much later elsewhere – use a dedicated Julian calculator for pre-Gregorian history.

999,999. The cap exists to bound the “nearest leap year” scan – the check itself is instant.

After the page loads, yes. HTML, CSS, and JS are self-contained – disconnect Wi-Fi and keep checking.