Gregorian calendar is used today? There are many calendars that have been used over the course of history. The Gregorian calendar is used today throughout much of the world. It uses the Christian religion to determine its starting point. However, in an effort to be more tolerant of all religions, many present-day scholars have begun using terms other than B.C. and A.D. (from the Gregorian calendar) to refer to dates. What are the new terms?