The calculation for when Pascha (aka Easter) occurs is different depending on if you use the Julian Calendar or the Gregorian Calendar. One matter that this article does not mention is that the *Revised Julian Calendar* was adopted in 1923 by various Orthodox churches that uses the Gregorian Calendar for all days except the Paschal calculation. - Ecumenical Patriarchate of Constantinople - Greek Orthodox Church - Romanian Orthodox Church - Bulgarian Orthodox Church - Orthodox Church in America (OCA) - Albanian Orthodox Church - Antiochian Orthodox Church - Cyprus Orthodox Church These are the churches that still use the original Julian Calendar: - Russian Orthodox Church - Serbian Orthodox Church - Georgian Orthodox Church - Jerusalem Orthodox Church - Polish Orthodox Church - Mount Athos (regardless of Constantinople's jurisdiction)