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
International Fixed Calendar The calendar year has 13 months with 28 days each, divided into exactly 4 weeks (13 × 28 = 364). An extra day added as a holiday at the end of the year (after December 28, i.e. equal December 31 Gregorian), sometimes called "Year Day", does not belong to any week and brings the total to 365 days. Each year coincides with the corresponding Gregorian year, so January 1 in the Cotsworth calendar always falls on Gregorian January 1. Twelve months are named and ordered the same as those of the Gregorian calendar, except that the extra month is inserted