How many days are in a year?
A common year has 365 days, and a leap year has 366. Earth takes about 365.24 days to orbit the Sun, so an extra day is added almost every four years.
Our calendar, the Gregorian calendar, adds February 29 in leap years to keep the calendar in step with Earth's orbit and the seasons. Without leap years, the calendar would drift by about one day every four years, and after a few centuries, summer months would fall in winter.
The calendar year is based on the tropical year, the time from one spring equinox to the next, which lasts about 365 days, 5 hours, 48 minutes and 45 seconds. Adding a leap day every four years overcorrects slightly, so century years are leap years only if divisible by 400. That is why 2000 was a leap year, but 1900 was not.
Other calendars
Not all calendars work the same way. The Islamic calendar follows the Moon and has about 354 or 355 days, so its months move through the seasons over time. The Hebrew and Chinese calendars combine lunar months with extra months to stay aligned with the solar year.
Did You Know?
The 2026 year is a common year with 365 days. The next leap year is 2028.