A leap year has 366 days.
This extra day is added to February, making it 29 days long instead of the usual 28. A leap year occurs every four years to help synchronize the calendar year with the solar year, which is about 365.24 days long. By adding an extra day every four years, we keep our calendars aligned with the seasons. However, there are exceptions to the rule: years that are divisible by 100 are not leap years unless they are also divisible by 400. This means that while the year 2000 was a leap year, 1900 was not.