As Catholics and most of the western world celebrated Easter a month ago, Jon Magoulias, an Eastern Orthodox priest, explains why the Orthodox Church doesn’t celebrate Pascha (Easter) on the same day the Catholic church does.

Here’s his well-documented explanation.

As Orthodox Christians prepare to celebrate Easter on Sunday, April 19th, we would like to shed some light on the reasons why the Orthodox Christian Church celebrates the Resurrection of Jesus Christ later than the Catholic one. While the issue is somewhat complicated, it may be summarized in the two factors at work that cause this conflict in dates:

1) The issue of the calendar.

2) The adherence by the Orthodox to the early practices of the Christian Church.

The first factor, the calendar, has to do with the fact that the Christian Orthodox Church continues to follow the Julian calendar when calculating the date of Pascha (Easter). The rest of Christianity uses the Gregorian calendar. There is a thirteen-day difference between the two calendars, the Julian calendar being thirteen (13) days behind the Gregorian.

The other factor at work is that the Orthodox Church continues to adhere to the rule set forth by the First Ecumenical Council, held in Nicea in 325 AD, that requires that Pascha must take place after the Jewish Passover in order to maintain the Biblical sequence of Christ’s Passion. The rest of Christianity ignores this requirement, which means that on occasion Western Easter takes place either before or during the Jewish Passover.

As a consequence of these two factors, the Orthodox Church usually celebrates Pascha later than the Western Churches – anywhere from one to five weeks later.

The two dates coincide when the full moon following the equinox comes so late that it counts as the first full moon after 21 March in the Julian calendar as well as the Gregorian. This is not a regular occurrence, but it has happened more frequently in recent years in 2010, 2011, 2014 and 2017, but, after that, not again until 2034.

For many people, this is a confusing and frustrating issue; especially, to those of us who have families that are not Orthodox wonder why we have to celebrate this important holiday at different times. In order to better understand why we do, we will take a closer look at how the date of Pascha is calculated and also examine the issue of the calendar.

How the Date of Pascha (Easter) is Determined

During the first three centuries of Christianity, there was no universal date for celebrating the Resurrection of Jesus Christ. Churches in various parts of the world followed different traditions. Some Christians celebrated Pascha on the first Sunday after Jewish Passover and others celebrated the feast at the same time as Passover.

In order to come up with one unified date for celebrating Pascha, the Holy Fathers of the First Ecumenical Council in 325 AD took up the issue. They devised a uniform formula for calculating the date of Pascha that was in line with the early traditions of the Church and the Biblical sequence of events.

The formula is this: Pascha is to be celebrated on the first Sunday, after the first full moon, following the vernal equinox, but always after Jewish Passover. In order to ensure that there was no confusion as to when the vernal equinox occurred the date of the vernal equinox was set to be March 21 (April 3 on the Julian Calendar). This formula was universally accepted by all of Christianity, ensuring that Pascha was celebrated on the same day throughout the world. The Orthodox Church continues to follow this formula exactly as prescribed by the Council of Nicea.

However, in modern times, the Western Church has rejected the part of the Nicene formula that requires that Pascha “always follow the Jewish Passover.” Western theologians (and, unfortunately, a few misguided Orthodox Theologians as well) now claim that this provision was never a part of the council’s intention, saying that it is not necessary for Pascha to follow the Jewish Passover.

This is hard to understand since, by rejecting this provision of the council, they ignore that the celebration of Jesus’ Resurrection was celebrated at the same time from 325-1582, as well as the written witness of early Church historians and even earlier canons such as Canon VII of the Apostolic Canons which reads: “If any Bishop, or Presbyter, or Deacon celebrate the holy day of Pascha before the vernal equinox with the Jews, let him be deposed.”

The Calendar Issue

In 1582 Pope Gregory XIII instituted a reform of the traditional Julian calendar. This new calendar, called the Gregorian calendar, was more astronomically correct and is the calendar used by most of the world today. As mentioned above, there is a difference of 13 days between the Gregorian and the Julian calendars. Eventually, all of the Western Churches adopted this “New” calendar. The Orthodox Church, however, vigorously opposed the use of the Gregorian calendar. This resulted in the West and East celebrating all Church feast days on different dates, the Orthodox celebrations always falling thirteen days behind the Western.

In 1923, an inter-Orthodox congress was held in Constantinople attended by representatives of some, but not all, Orthodox churches. This Congress made the very controversial decision to follow a revised calendar that was essentially the same as the Gregorian calendar, for all things except the celebration of Pascha, which continued to be calculated according to the original Julian calendar.

The result is that today we celebrate most feast days, like Christmas, Epiphany and the rest, at the same time as Western Christians and only Pascha and the feast days that are connected with it like Pentecost and the Ascension, are dated according to the Julian calendar and celebrated on different dates. For Orthodox, it is important to maintain the teachings and traditions of the Church intact and pure.