February 29 is followed by February 30 in Sweden, in a move to abolish the Swedish calendar for a return to the Julian calendar.

Several non-standard dates are used in calendars for various purposes: some are expressly fictional, some are intended to produce a rhetorical effect, and others attempt to address a particular mathematical, scientific or accounting requirement or discrepancy within the calendar system.

The Swedish calendar or Swedish style was a calendar in use in Sweden and its possessions from 1 March 1700 until 30 February 1712. It was one day ahead of the Julian calendar and ten days behind the Gregorian calendar. Easter was calculated astronomically, with a minor exception, from 1740 to 1844.

The Julian calendar is a solar calendar of 365 days in every year with an additional leap day every fourth year. The Julian calendar is still used as a religious calendar in parts of the Eastern Orthodox Church and in parts of Oriental Orthodoxy as well as by the Amazigh people. For a quick calculation, between 1901 and 2099 the much more common Gregorian date equals the Julian date plus 13 days.

February 29 is a leap 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 only. 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.