What Is a Leap Year?
Definition
Leap Year: A year of 366 days, with 29 days in February. In the Gregorian calendar, years divisible by 4 are leap years, except century years not divisible by 400.
A leap year is a year of 366 days, with 29 days in February. In the Gregorian calendar, years evenly divisible by 4 are leap years, except century years that 400 does not divide evenly. The rule keeps the calendar in step with the solar year. The age and date calculators count the extra day.
Where it appears in the formulas
leap year = (year divisible by 4 and not by 100) or (year divisible by 400). So 1700, 1800, 1900 and 2100 are not leap years, while 1600, 2000 and 2400 are. The average Gregorian year is 365.2425 days. The age calculator, the date difference calculator and the day counter give February 29 days in leap years.
Birthdays on 29 February
A common year has no 29 February. The age calculator counts the birthday on 1 March in those years. No Turkish law settles this; 1 March is the common practice in Türkiye.