Leap Year Checker

Leap Year Checker

Check a Single Year

Please enter a valid year (1–9999).

Find All Leap Years in a Range

Please enter a valid range (max 500 years).

Next 5 Upcoming Leap Years

Leap Year Checker – Is It a Leap Year?

A leap year is a calendar year containing 366 days instead of the usual 365. The extra day, February 29th (called leap day), keeps our calendar synchronized with Earth's orbit around the Sun. Our leap year checker tells you instantly whether any year is a leap year, explains exactly why using the divisibility rules, and even lists all leap years within a range you specify.

The Rules for Determining a Leap Year

The Gregorian calendar (in use since 1582) uses three rules to determine leap years:

  • A year divisible by 4 is a leap year — e.g., 2024, 2028.
  • However, a year divisible by 100 is not a leap year — e.g., 1900 was not a leap year.
  • Exception: a year divisible by 400 is a leap year — e.g., 2000 and 2400 are leap years.

This three-tier rule corrects the slight overcount that the simple "÷4" rule would cause, keeping the calendar accurate to within 26 seconds per year.

Why Do We Have Leap Years?

Earth takes approximately 365.2422 days to orbit the Sun — not a neat 365. Without adjustment, our calendar would drift roughly one full day every 4 years. Over centuries, seasons would shift: December would eventually occur in summer in the Northern Hemisphere. Julius Caesar introduced the concept of the leap year in 46 BC with the Julian Calendar (simply every 4th year). Pope Gregory XIII refined it in 1582 with the century-year exceptions, creating the Gregorian Calendar we use today.

How Leap Day Affects People

People born on February 29 — called "leaplings" or "leap year babies" — officially celebrate their birthday only every 4 years. In non-leap years, most leaplings celebrate on either February 28 or March 1, depending on local custom and legal definitions. The odds of being born on Feb 29 are roughly 1 in 1,461.

Calendar History and Reform

Before the Gregorian reform, the Julian Calendar's simpler rule (every 4 years without exception) caused the calendar to drift about 11 minutes per year. By 1582, it had drifted 10 days from the astronomical equinox. Pope Gregory skipped 10 days (October 4, 1582 was followed by October 15) to realign, and introduced the century-year exception going forward.

Frequently Asked Questions

Was the year 2000 a leap year?
Yes. The year 2000 is divisible by 400, so it is a leap year. This is why many people incorrectly remember 1900 as a leap year — 1900 is divisible by 100 but not by 400, so it was not a leap year.
When is the next leap year?
Leap years occur every 4 years (with the century exceptions). After 2024, the next leap years are 2028, 2032, 2036, and 2040. Use the tool above to see the upcoming 5 from today.
How many leap years are there in a century?
In a typical century there are 24 leap years (every 4 years = 25, minus the century year that is not divisible by 400). For a century ending in a year divisible by 400 (like 2000), there are 25 leap years.
What happens to software on leap day?
Software bugs related to leap day are historically significant. In 2012, Microsoft Azure experienced a major outage on February 29 due to a date calculation bug. Proper date libraries handle leap years automatically, but custom date math in code often misses edge cases.
Can I check very old years like 1066?
Yes, the tool applies the Gregorian rules to any year you enter. Note that the Gregorian calendar was only adopted in 1582 — for years before that, the Julian calendar was in use, which had slightly different rules (no century-year exception).