February 29

February 29 is a leap day (or "leap year day")—an intercalary date added periodically to create leap years in the Julian and Gregorian calendars. It is the 60th day of a leap year in both Julian and Gregorian calendars, and 306 days remain until the end of the leap year. It is the last day of February in leap years and does not exist in common years. It is also the last day of meteorological winter in the Northern Hemisphere and the last day of meteorological summer in the Southern Hemisphere in leap years.

In the Gregorian calendar, the standard civil calendar used in most of the world, February 29 is added in each year that is an integer multiple of four, unless it is evenly divisible by 100 but not by 400. For example, 1900 was not a leap year, but 2000 was. The Julian calendar—since 1923 a liturgical calendar—has a February 29 every fourth year without exception. Consequently, February 29 in the Julian calendar, since 1900, falls 13 days later than February 29 in the Gregorian, until the year 2100.^[1]

The convention of using February 29 was not widely accepted before the 15th century; from Julian's edict until the 16th century (formally), February 24 was doubled instead.^[2] In one of its attempts to adopt the Gregorian calendar, Sweden tried (unsuccessfully) to phase in the change by omitting leap days in the 11 successive leap-years, 1700–1740.^[3]