Orthodox Easter in 2018 is on Sunday, April 8.
The Orthodox call this day Pascha. It is the most joyous celebration of the entire year, as the community gathers together to celebrate the Resurrection of Jesus Christ.
How is the date for Orthodox Easter calculated?
In 325 AD the First Ecumenical Council established a unified observance of Orthodox Easter (i.e. Pascha). It decreed that Pascha would be held on the first Sunday after the first full moon occurring on or after the vernal equinox. March 21 is used as an approximation of the vernal equinox. Pascha is delayed by a week if the full moon is on Sunday.
Why is Easter and Pascha on different dates?
While Pascha and the western Easter are both calculated using the same formula, the end dates often differ because they have different starting points. Orthodox Churches still use the Julian calendar as the starting point for the Pascha calculation.
While most Orthodox Churches adopted the modern Gregorian calendar, some retained the Julian. To maintain unity within the entire church, all Orthodox celebrate the feast of feasts on the same day through-out the world.
The old Julian solar calendar is 13 days behind the Gregorian’s and its lunar calendar is four to five days behind, causing the date for Pascha to often fall on a different date to that of Easter.
While Pascha normally falls either one or five weeks later than Easter, on occasion they can be four weeks apart and on some years the dates of Pascha and Easter coincide. The dates coincided most recently in 2017 and the next coincidence will be in 2025.