Leap year before 1, but only if the year is expressed with astronomical year numbering. It is not valid for the BC or BCE notation. The algorithm is not necessarily valid for years in the Julian calendar, such as years before 1752 in the British Empire. The year 1700 was a leap year in the Julian calendar, but not in the Gregorian calendar. February 29 is a date that usually occurs every four years, and is called leap day. This day is added to the calendar in leap years as a corrective measure, because the Earth does not orbit the sun in
Century leap year Century leap year In the Gregorian calendar, a year ending in "00" that is divisible by 400 is a century leap year, with the intercalation of February 29 yielding 366 days instead of 365. Century years (divisible by 100) that are "not" divisible by 400 are not leap years but common years of 365 days. For example, the years 1600, 2000, and 2400 are century leap years since those numbers are divisible by 400, while 1700, 1800, 1900, 2100, 2200, and 2300 are common years despite being divisible by 4. Leap years divisible by 400 always start on a Saturday;