2024 is a leap year with 366 days. Leap day is added to the end of February every four years, making it 29 days long. Leap years and days keep the calendar in sync with the seasons as the Earth takes about 365.2422 days to orbit the Sun. The rule to determine a leap year is that it should be divisible by four, except if it is divisible by 100, unless it is also divisible by 400. February was chosen as the month for leap day due to Julius Caesar's reforms.