Leap Year Calculator

How to Use the Leap Year Calculator

The Leap Year Calculator instantly determines whether any year is a leap year and shows you the next upcoming leap year. It also lists all leap years within any range and explains the rules behind this calendar adjustment that keeps our calendar aligned with Earth orbit around the Sun.

How to Check

Enter any year in the input field and click Check. The calculator tells you whether it is a leap year and explains why based on the rules. You can also enter a range of years to see a complete list of leap years within that period.

Leap Year Rules

A year is a leap year if it follows these rules in order:

1. If the year is divisible by 4, it is a leap year.

2. However, if the year is also divisible by 100, it is NOT a leap year.

3. However, if the year is also divisible by 400, it IS a leap year.

So 2024 is a leap year (divisible by 4). 1900 was NOT a leap year (divisible by 100 but not 400). 2000 WAS a leap year (divisible by 400).

Why Leap Years Exist

Earth takes approximately 365.2422 days to orbit the Sun. A standard calendar year of 365 days falls short by about 0.2422 days. Without correction, the calendar would drift by about 24 days per century. Adding a leap day every 4 years (with the century exceptions) keeps the calendar year synchronized with the astronomical year to within one day per 3,236 years.

Leap Year Effects

In a leap year, February has 29 days instead of 28, making the year 366 days long. People born on February 29 (called leaplings) celebrate their birthday on February 28 or March 1 in non-leap years. The next leap years are 2024, 2028, 2032, 2036, and 2040.

Frequently Asked Questions

Q: Why was 2000 a leap year but 1900 was not?

A: The century rule (divisible by 100 = not a leap year) removes too many leap years, overcorrecting the calendar. The 400-year exception adds back the necessary adjustment. Years 1600 and 2000 were leap years; 1700, 1800, and 1900 were not; 2100, 2200, and 2300 will not be.

Q: How often do leap years occur?

A: Leap years occur every 4 years on average, but not exactly. In a 400-year cycle, there are 97 leap years (not 100), because three century years out of four are excluded. The average year length becomes 365.2425 days, very close to the actual orbital period of 365.2422 days.

Q: What happens to people born on February 29?

A: Leaplings legally age one year each year like everyone else. For legal purposes, most jurisdictions treat March 1 as their birthday in non-leap years. Some celebrate on February 28 instead. They technically experience their actual birth date only every 4 years, making a 40-year-old leapling someone who has had only 10 actual birthdays.