Since AD1582 October (when the Gregorian Calendar was adopted by much of Catholic Europe), the Orthodox Easter usually falls on dates different than the Western Christian Easter, although apparently the Churches are discussing using the same formula to determine Easter - probably a formula different than that currently used by either Church.

The Orthodox Easter is determined in the Julian Calendar. It has been claimed that Orthodox Easter does not fall on the date of Passover (15 Nisan in the Hebrew Calendar), or before it; this is true recently, but using the modern formulae for determining the date of Passover (rules which go back to the fourth century A.D.), one finds that, in fact, Easter occurred on the first day of Passover several times before the year A.D. 1000. From 1900 until 2099 the Eastern Easter will fall one (45.5%), four (4.5%), or five (21.5%) weeks after the Western Easter - and on the same date in 57 (28.5%) of those years. (I've compiled some Tables showing the offsets between Orthodox and Western Easters from 1583 through 3000 that shows this information.)

RMD(x,y) = remainder when x is divided by y.

R1=RMD(Year,19)

R2=RMD(Year,4)

R3=RMD(Year,7)

RA=19*R1+16

R4=RMD(RA,30)

RB=2*R2+4*R3+6*R4

R5=RMD(RB,7)

RC=R4+R5

The number RC ranges from 1 to 35 which corresponds to March 22 to April 25 in the Julian Calendar (currently April 4 to May 8 on the Gregorian). The Julian Calendar is now 13 days behind the Gregorian, and will be until March 1, 2100 when it will be 14 days behind the Gregorian Calendar.

Copyright and disclaimer ------------------------ This document is Copyright (C) 1996 by Claus Tondering. E-mail: c-t@pip.dknet.dk. The document may be freely distributed, provided this copyright notice is included and no money is charged for the document. This document is provided "as is". No warranties are made as to its correctness. 2.9.6. Isn't there a simpler way to calculate [Orthodox] Easter? ----------------------------------------------------- This is an attempt to boil down the information given in the previous sections (the divisions are integer divisions, in which remainders are discarded): [Note: 22%7=1 ; 22/7=3, so % returns the remainder, and / neglects the remainder.] G = year % 19 I = (19*G + 15) % 30 J = (year + year/4 + I) % 7 L = I - J EasterMonth = 3 + (L + 40)/44 EasterDay = L + 28 - 31*(EasterMonth/4) [Note: Orthodox Easter is then EasterDay of EasterMonth in the Julian Calendar. You will need to add the correct offset to obtain the date in the Gregorian Calendar. From Julian Mar 1, 1900, to Julian Feb 29, 2100, the correction is to add 13 days to the Julian date to obtain the Gregorian date.] This algorithm is based in part on the algorithm of Oudin (1940) and quoted in "Explanatory Supplement to the Astronomical Almanac", P. Kenneth Seidelmann, editor. People who want to dig into the workings of this algorithm, may be interested to know that G is the Golden Number-1 I is the number of days from 21 March to the Paschal full moon J is the weekday for the Paschal full moon (0=Sunday, 1=Monday, etc.) L is the number of days from 21 March to the Sunday on or before the Pascal full moon (a number between -6 and 28)

Using these algorithms, I have made tables for the date of Orthodox Easter, tabulated in both the Julian and Gregorian calendars for AD 1875-2124.

Carter's algorithm, Butcher's algorithm, and Oudin's algorithm are algorithms for the Western Churches.

Days before Easter Days after Easter Triodon 70 Ascension 39 Sat. of Souls 57 Sat. of Souls 48 Meat Fare 56 Pentecost 49 2nd Sat. of Souls 50 All Saints 56 Lent Begins 48 St. Theodore 43 Sun. of Orthodoxy 42 Sat. of Lazarus 8 Palm Sunday 7 Good Friday 2

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Last updated 2000 April 7.

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