Leap day

A year is not exactly equal to 365 days, but lasts approximately 365 days and six hours. To make up for this, every year of which the last to two digits are divisible by 4 or by 400, if it is the first year of a new century, an extra day is intercalated. The leap day is invariably the 29th of February. A leap year has 366 days as opposed to a common or non-leap year, which has 365 days.