A leap year has 366 days instead of 365: February has 29 days. These extra days keep our calendar in sync with Earth's orbit around the Sun (~365.2422 days).

What is the rule for leap years?

A year is a leap year if: (1) divisible by 4, AND (2) if divisible by 100, must also be divisible by 400. So 2000 was a leap year, but 1900 was not.

Why is 2100 not a leap year?

2100 is divisible by 100 but NOT by 400, so it is not a leap year. The next century leap year is 2400.

How often do leap years occur?

Approximately every 4 years. However, century years (1800, 1900) are skipped unless divisible by 400, giving 97 leap years per 400-year cycle.

Leap Year Calculator

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Documentation

The Leap Year Rule

The Gregorian calendar uses a 400-year cycle. A leap year adds one February 29 to keep the calendar synchronized with Earth's ~365.2422-day orbit around the Sun.

Algorithm

IF (year % 4 == 0)

AND NOT (year % 100 == 0)

OR (year % 400 == 0)

THEN leap year

Disclaimer: Based on the Gregorian calendar system.

Frequently Asked Questions

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Check if any year is a leap year and find upcoming leap years. Enter your values above to get instant results from this free online leap year calculator.

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Leap Year Calculator

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The Leap Year Rule

Algorithm

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