Between 1582 and 1752, Catholic countries used the Gregorian calendar, while Britain and her colonies used the Julian calendar. To convert British and Catholic dates occurring between 1582 and 1752, it is necessary to change calendars from Julian to Gregorian.

George Washington was born on February 22, 1732. In France, the date was:

Voltaire was born on November 21, 1694. In Great Britain the date was:

The Russian Orthodox Church still uses the Julian calendar. This finds the Western (Gregorian) date of Greek Orthodox Christmas 2000:

The Julian calendar has a four-year cycle with 1461 days:

Russian Orthodox dates are computed according to the Julian calendar. This program returns the standard Western (Gregorian) date for Russian Orthodox Christmas for the given Russian Orthodox year: