Proleptic Gregorian calendar Julian and proleptic Gregorian calendar dates are as follows: The table below assumes a Julian leap day of 29 February, but the Julian leap day (the bissextile day) was in Latin or 24 February (see Julian reform), so dates between 24 and 29 February in all leap years were irregular. Note: When converting a date in a year which is leap in one calendar but not the other, include 29 February in the calculation when the conversion crosses the border between February and March. Proleptic Gregorian calendar The proleptic Gregorian calendar is produced by extending the Gregorian calendar backward to
Adoption of the Gregorian calendar against a horizontal time line. The vertical axis is used for expansion to show separate national names for ease in charting, but otherwise has no significance. Adoption of the Gregorian calendar The adoption of the Gregorian Calendar was an event in the modern history of most nations and societies, marking a change from their traditional (or "old style") dating system to the modern (or "new style") dating system that is widely used around the world today. Some countries adopted the new calendar from 1582, some did not do so before the early twentieth century, and others did so at various