Check Leap Year Online Free Tool
Check whether a year is a leap year. Gregorian divisibility breakdown + nearest leap years before and after. Free, client-side, instant.
Enter any year 1–999,999 and get a Gregorian leap vs common verdict, divisibility breakdown, and the nearest leap-year neighbours.
Divisibility breakdown
Leap rule: divisible by 4, except century years which must also be divisible by 400.
Nearest leap years
How to Use Check Leap Year Online Free Tool
- Type a year (1 to 999,999) into the input field, or click
Use current yearto fill in today's value. - Watch the verdict update 150 ms after you stop typing - amber means leap, green means common.
- Inspect the breakdown card for the three yes-no rows (÷4, ÷100, ÷400). Leap years are divisible by 4 AND (not ÷100 OR also ÷400).
- Check the nearest leap years card for the closest leap year before and after your input - handy for planning February 29 events.
- Press
Ctrl+Enter(⌘+Enteron Mac) to force a check at any time. - Copy the summary to your clipboard or Download a timestamped `.txt` report.
Frequently asked questions
How do you know if a year is a 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.
What is 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.
Is my data uploaded anywhere?
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.
Why was 2000 a leap year but not 1900?
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.
What does the divisibility breakdown show?
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.
How often do leap years occur?
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.
Why are the nearest leap years useful?
For scheduling February 29 events or checking contract anniversaries. The tool scans up to the 999,999-year cap in each direction.
Does it work for years before 1582?
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.
What’s the largest year I can check?
999,999. The cap exists to bound the “nearest leap year” scan – the check itself is instant.
Does it work offline?
After the page loads, yes. HTML, CSS, and JS are self-contained – disconnect Wi-Fi and keep checking.