Leap Year Calculator
Check if any year is a leap year and find the next or previous one
Leap Year Calculator
Check if a year is a leap year
Enter a year
Leap if divisible by 4 AND (not by 100, OR by 400)What Is a Leap Year?
A leap year has 366 days instead of the usual 365 — the extra day is February 29, also called a leap day. Leap years exist because Earth takes approximately 365.2422 days to orbit the sun. If we always used a flat 365-day calendar year, our calendar would slowly drift out of alignment with the seasons by about one full day every four years — meaning winter would creep into what we call autumn within a few centuries.
In the Gregorian calendar — the system used worldwide since its adoption in 1582 — a year is a leap year if it is divisible by 4, with one important exception: century years (divisible by 100) are NOT leap years unless they are also divisible by 400. That is why the year 2000 was a leap year, but 1900 was not, and 2100 will not be either.
How to Use the Leap Year Calculator
- 1Enter any year in the input field (for example, 2024, 1900, or 3000).
- 2Click the Check button or press Enter.
- 3The result tells you immediately whether the year is a leap year.
- 4Below the result you will also see the nearest previous leap year and the next upcoming leap year.
The Leap Year Formula Explained
A year is a leap year if: (year % 4 == 0) AND (year % 100 != 0) OR (year % 400 == 0) Simplified rule: Leap if: divisible by 4 EXCEPT: century years (÷100) are NOT leap UNLESS: also divisible by 400 → IS leap Examples: 2024: 2024 ÷ 4 = 506, not a century → YES (leap) 1900: 1900 ÷ 100 = 19, not ÷ 400 → NO 2000: 2000 ÷ 400 = 5 → YES (leap) 2100: 2100 ÷ 100 = 21, not ÷ 400 → NO
The Gregorian calendar adds a leap day every four years to keep in sync with Earth's 365.2422-day solar year. However, 365.2422 is slightly less than 365.25, so the simple 'divide by 4' rule overcounts by about 3 days every 400 years. Skipping leap years on century years — unless they are divisible by 400 — corrects for that overcount and keeps the calendar accurate to within 26 seconds per year.
Worked Examples
2024 — Leap Year
2024 is divisible by 4 (2024 ÷ 4 = 506) and is not a century year, so it is a leap year. February 2024 had 29 days. The next leap year after 2024 is 2028.
1900 — Not a Leap Year
1900 is divisible by 4 and by 100, making it a century year. However, 1900 is not divisible by 400 (1900 ÷ 400 = 4.75), so the century exception applies and 1900 is NOT a leap year. February 1900 had only 28 days.
2000 — Leap Year
2000 is a century year (divisible by 100), but it is also divisible by 400 (2000 ÷ 400 = 5), so the 400-year override kicks in and 2000 IS a leap year. This made the year 2000 special — many people assumed it would not be a leap year, but it was.
Frequently Asked Questions
What happens to people born on February 29?
People born on February 29 — sometimes called 'leaplings' or 'leap year babies' — officially celebrate their birthday only once every four years. In non-leap years they typically celebrate on February 28 or March 1, depending on personal preference and local laws. In some countries, legal documents treat February 28 as the official birthday in non-leap years.
Why does the Gregorian calendar use the 400-year rule?
Earth's solar year is 365.2422 days, not exactly 365.25. Adding a leap day every 4 years (365.25 average) overshoots by 0.0078 days per year — roughly 3 extra days every 400 years. To correct this, the Gregorian calendar skips 3 leap years every 400 years by making century years non-leap, unless divisible by 400. The result is an average of 365.2425 days per year, accurate to within about 26 seconds of the true solar year.
Are there other calendar systems with different leap year rules?
Yes. The Julian calendar (used before the Gregorian reform) simply adds a leap day every 4 years with no century exception, which causes it to drift by about 1 day every 128 years. The Hebrew calendar adds an extra month (not just a day) 7 times every 19 years. The Islamic (Hijri) calendar is a purely lunar calendar with no leap-year solar correction at all, which is why Islamic holidays shift through the seasons over time.
How many leap years are there in a 100-year period?
In most 100-year spans there are 24 or 25 leap years. Specifically, in any given century starting on a non-400-divisible year (like 1901–2000 or 2001–2100) there are 24 leap years — the century year itself is skipped. In the special century that includes a 400-divisible year (like 2000), that year counts, giving 25 leap years in that span.
What was the Julian calendar's leap year rule and why was it changed?
The Julian calendar, introduced by Julius Caesar in 45 BC, used a simple rule: every year divisible by 4 is a leap year, with no exceptions. Over time this caused the calendar to drift forward by about 10 days relative to the solar year. Pope Gregory XIII corrected this drift in 1582 by introducing the Gregorian calendar with the 100/400 exception. Countries adopted the new calendar at different times — Britain and its colonies (including America) switched in 1752.