The Gregorian calendar is the internationally accepted civil calendar. It was first proposed by the Calabrian doctor Aloysius Lilius, and decreed by Pope Gregory XIII, after whom the calendar was named, on 24 February 1582 by the papal bull Inter gravissimas. It is a reform of the Julian calendar.

Gregory's bull does not ordain any particular year-numbering system, but uses the Anno Domini system which counts years from the traditional Incarnation of Jesus, and which had spread throughout Europe during the Middle Ages. That is the same year-numbering system that is the de facto international standard today. The Gregorian calendar modifies the Julian calendar's regular four-year cycle of leap years as follows:

Similar to 0 things you like: