Century leap year

In the Gregorian calendar, a century leap year is a year that is exactly divisible by 400. Like all other leap years, these years have February 29. If a year is divisible by 100 but not 400, it is a common year (not a leap year). For example, the years 1600 and 2000 were century leap years; the century years 1700, 1800, 1900 were common years, so will 2100, 2200, and 2300, despite being divisible by 4. The next century leap year will occur in the year 2400. Century leap years always begin on a Saturday, and February 29 always falls on a Tuesday.

The start days of exceptional common years (century years not evenly divisible by 400) also varies; the century year begins on a Friday if the remainder obtained by dividing it by 400 is 100, Wednesday if the remainder is 200, and Monday if the remainder is 300.

The Gregorian calendar more accurately tracks Earth's revolution around the Sun, more so than the older Julian calendar, in which every fourth year (including end-of-century years) is a leap year. Because of this, the Julian calendar began to gradually drift with respect to the four seasons. Each season has been occurring earlier and earlier over time. Therefore when the Gregorian calendar was created in 1582, it eliminated this problem by specifying that end-of-century years are only leap years if divisible by 400. Therefore, 1700 was the first end-of-century year that was not a leap year.