Revised Julian calendar
The following are Gregorian minus Revised Julian date differences, calculated for the beginning of January and March in each century year, which is where differences arise or disappear, until AD 10000. These are exact arithmetic calculations, not depending on any astronomy. A negative difference means that the proleptic Revised Julian calendar was behind the proleptic Gregorian calendar. The Revised Julian calendar is the same as the Gregorian calendar from 1 March 1600 to 28 February 2800, but the following day would be 1 March 2800 (RJ) or 29 February 2800 (G); this difference is denoted as '+1' in the table. 2900 is a leap year in Revised Julian, but not Gregorian: 29 February 2900 (RJ) is the same as 28 February 2900 (G) and the next day will be 1 March 2900 in both calendars - hence the '0' notation.