Although there are exceptions, a leap year occurs once every four years in order to keep the calendar year properly synchronized with the astronomical or seasonal year. The necessity for leap years arises from the fact that a year on Earth is actually about 365 and 1/4 days long. A leap year has a total of 366 days, instead of the usual 365 as a result of adding an extra day (February 29) to the Gregorian calendar. The Gregorian calendar is the calendar format currently used by most modern societies. The New Style (N.S.) or Gregorian calendar was introduced in 1582, to replace the flawed Old Style (O.S.) or Julian calendar, though the adoption of this new calendar was not universally concurrent, with many nations delaying its implementation several centuries.

Leap year guidelines
Any year evenly divisible by four is a leap year, except centesimal years (years ending in two zeros) which are considered common years and thus have the typical 365 days, unless they are evenly divisible by 400. Therefore, 1600 and 2000 are leap years, while 1700, 1800, 1900 and 2100 are not. This leap year system helps ensure the calendar coincides with the cycle of the seasons.

Below you will find a list of all leap years between 1800 and 2100. Each of these years is also a link to a 12-month calendar for the year noted. Remember, 1800, 1900 and 2100 are not leap years. Visit our calendar index for links to perpetual calendars for any year (including non-leap years) between 1801 and 2100.

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