What is a leap year?
A leap year is a year in which February has 29 days instead of 28. Since it takes Earth about 365.2422 days β not exactly 365 β to orbit the sun, an extra day is added every 4 years to correct for that difference.
The rule
- A year is a leap year if it's divisible by 4.
- However, a year divisible by 100 is not a leap year.
- Except that a year divisible by 400 is a leap year after all.
This extra exception for multiples of 100 exists because adding one day every 4 years alone would slightly overcorrect compared to Earth's actual orbital period. For example, 1900 was not a leap year, but 2000 was, because it's a multiple of 400.
Want to calculate a countdown too?
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Frequently Asked Questions
How do people born on February 29 celebrate their birthday?
Since February 29 doesn't exist in non-leap years, many people celebrate on February 28 or March 1 instead. Legally, different countries may set different official dates for this.
Does the lunar calendar have a similar concept?
Yes β the lunar calendar uses leap months (adding an entire extra month every few years) to correct for the difference with the solar year. The mechanism is different from the solar calendar's leap year.