Rules of dating when separated
The following algorithm will compute the date of Easter using the Gregorian Calendar.
The new calendar was issued in February in the papal bull called "Inter gravissimas".
By the 1700's, though, most of western Europe had adopted the Gregorian Calendar.
The Eastern Christian churches still determine the Easter dates using the older Julian Calendar method.
See our FAQ on Calendars for a description of the difference.
Universal adoption of this Gregorian calendar occurred slowly.