How this calculator works
Enter any year to find out whether it is a leap year, which rule of the Gregorian calendar decided that, how many days it contains, and — if it is a leap year — which day of the week February 29 falls on. The tool also lists the five leap years immediately before and after the one you entered, which is useful for spotting the irregular gaps around century years.
The leap year rule exists to keep the calendar aligned with Earth's orbit around the Sun, which takes about 365.2425 days, not an even 365. Adding an extra day roughly every 4 years accounts for most of that discrepancy, but a plain ÷4 rule would overcorrect slightly, so the calendar skips 3 leap years every 400 years by excluding century years that are not divisible by 400.
The Gregorian leap year rule
1. If the year is divisible by 400 → leap year.2. Else if the year is divisible by 100 → not a leap year.3. Else if the year is divisible by 4 → leap year.4. Otherwise → not a leap year.This is the rule that has governed the civil calendar since Pope Gregory XIII's 1582 reform; the older Julian calendar used only the simple ÷4 rule, which is why Julian and Gregorian leap years diverge on century years.
Worked example: 1900, 2000 and 2100
- 1900 ÷ 4 = 475 exactly, so the simple rule would call it a leap year — but 1900 ÷ 100 = 19 exactly and 1900 ÷ 400 = 4.75, not exact, so the century exception makes 1900 NOT a leap year.
- 2000 ÷ 100 = 20 exactly, but 2000 ÷ 400 = 5 exactly too, so the exception-to-the-exception applies and 2000 IS a leap year — 366 days, with February 29 falling on a Tuesday.
- 2100 ÷ 100 = 21 exactly and 2100 ÷ 400 = 5.25, not exact, so like 1900, 2100 will NOT be a leap year — the next one after 2096 will be 2104.
- By contrast, 2024 ÷ 4 = 506 exactly and it is not a century year, so no exception applies: 2024 is a leap year, with February 29 falling on a Thursday.
Frequently asked questions
Why isn't 1900 a leap year if it's divisible by 4?
Century years (ending in 00) follow a stricter test: they must be divisible by 400, not just 4. 1900 ÷ 400 = 4.75, so the century exception overrides the simple ÷4 rule and 1900 is not a leap year. The same applies to 2100, 2200 and 2300.
Why is 2000 a leap year, then, since it's also a century year?
2000 ÷ 400 = 5 exactly, so it passes the stricter century test. This makes 2000 an 'exception to the exception' — a century year that is still a leap year, which happens only once every 400 years (1600, 2000, 2400, ...).
How many leap years are there in 400 years?
97. A naive ÷4 rule would give 100 leap years in 400 years, but the century rule removes 3 of them (like 1700, 1800, 1900), leaving 97 — which keeps the calendar average at 365.2425 days per year, very close to the true 365.2422-day solar year.
What happens to someone born on February 29 in a non-leap year?
There is no February 29 to celebrate on, so most people born on a leap day mark either February 28 or March 1 in common years. This calculator's related Next Birthday Calculator states explicitly which convention it uses for that case.
Does every calendar use the same leap year rule?
No — this is specifically the Gregorian calendar rule used by the civil calendar in almost every country today. Other calendars (Julian, Hebrew, Islamic, Chinese) have entirely different leap year or leap month systems, some using simpler ÷4 rules and others intercalating extra months rather than extra days.