Leap Year Checker
Instantly check whether any year is a leap year, see why, how many days it has, and the next leap years — runs 100% in your browser with no upload.
2024 is a leap year. Divisible by 4 but not by 100 → leap year Days in this year: 366 Next 5 leap years: 2028, 2032, 2036, 2040, 2044
🔒 Calculated in your browser — nothing is uploaded.
What this tool does
Type any year and this tool instantly tells you whether it is a leap year or a common year, and explains exactly which rule applied. It also shows how many days that year has — 366 for a leap year and 365 for a common year — and lists the next five leap years so you can plan ahead. The Gregorian leap year rule is simple but has a twist: a year is a leap year if it is divisible by 4, except for years divisible by 100, unless they are also divisible by 400. That is why 2000 is a leap year but 1900 is not, and why 2024 is a leap year while 2023 is not.
Why the leap year rule works this way
Earth takes about 365.2422 days to orbit the Sun, so adding one extra day every four years keeps the calendar roughly aligned with the seasons. But four years of quarter-days slightly overshoots, so the Gregorian calendar skips the leap day in three out of every four century years — keeping years divisible by 400 like 1600 and 2000, but dropping 1700, 1800 and 1900. This 97-leap-days-per-400-years scheme keeps the calendar accurate to within about one day every 3,000 years. Everything here is computed locally in your browser, so you can check as many years as you like without limits.
Frequently asked questions
Why is 2000 a leap year but 1900 is not?
Both are divisible by 4 and by 100, which by itself would make them common years. The extra rule says century years are leap years only when also divisible by 400. 2000 is divisible by 400, so it is a leap year; 1900 is not divisible by 400, so it is a common year.
How many days are in a leap year?
A leap year has 366 days because February gains a 29th day. A common (non-leap) year has 365 days. This tool shows the exact day count for whichever year you enter.
Is the year I type sent to a server?
No. Everything runs entirely in your browser using JavaScript. The year you enter and every result are calculated on your device — nothing is uploaded, logged, or stored.