Why does the date of Easter change every year?
Unlike other Christian celebrations such as Christmas, Easter is different in that the date it falls on changes every year. Not only that, but other dates that relate to Easter Sunday (like the start and end of Lent, Good Friday and Palm Sunday ), change each year as a result.
As if this isn’t confusing enough, you then need to add into the mix that the date of Easter can fall on a different day in the same year depending on whether you’re following Western Christianity or Eastern Orthodox Christianity. Western Christianity uses the Gregorian calendar, whilst Eastern Orthodox Christianity follows the the Julian calendar.
To help demystify why the date of Easter changes we’ve pulled together the facts to explain the history and reasoning behind it all.
The date of Easter was originally tied to the Jewish festival of Passover
The date of Easter was originally calculated according to the time of Jesus’ death and resurrection, which occurred around the time of Jewish Passover. Passover is celebrated in early spring, from the 15th through to the 22nd of the Hebrew month of Nissan.
Early believers wished to keep the observance of Easter related to Passover to ensure Easter celebrations occurred after this date.
Because the Jewish holiday calendar is set using solar and lunar cycles, each feast day moves every year. As a consequence Easter also gained it’s status as a moveable feast (i.e. one that falls on a different date each year).
In 325 AD the Council of Nicea standardised the way to set the date of Easter
Come 325 AD the Council of Nicea* decided to create a standardised system for determining when Easter would fall. They created a table of Ecclesiastical Full Moon** dates by which Holy Days on the Ecclesiastical calendar were set.
The Council established that Easter would now now fall on the first Sunday following the Paschal Full Moon occurring on or after 21 March (the Vernal or Spring Equinox). Thereby creating a uniform observance of this date across Western Christianity.
To avoid the possibility of Easter falling on the same day as the Jewish Passover, they ruled that the date of Easter Sunday is delayed by 1 week if the full moon is on a Sunday.
*The Council of Nicea were the first ecumenical council, convened by the Roman Emperor Constantine, to attain consensus in the church through an assembly representative all of Christendom.
**This “full moon” does not currently correspond directly to any astronomical event, but is instead the 14th day of a lunar month, determined from tables. It may differ from the date of the actual full moon by up to two days.
The date of Easter can fall between late March to late April
Easter can fall anytime between 22 March to 25 April. This is due to the way in which the date of Easter is calculated according to the rules established by the Council of Nicea.
If the Paschal Full Moon falls on Saturday 21 March, Easter would be the following day – Sunday 22 March. The earliest possible date for Easter.
If the Paschal Full Moon falls on Saturday 20 March, the day before the Spring Equinox, Easter would not fall until after the next full moon. This can make the date of Easter as late as Sunday 25 April.
Eastern Orthodox Easter and Western Easter fall on different dates
As mentioned previously, the date of Easter can also change depending on whether you’re following Eastern or Western Christianity.
Everybody in the Roman world, including the early Christians used to use the ‘Julian’ Calendar (which had been popularised by no less a man than Julius Caesar himself).
However, as the centuries passed, people began to notice that the calendar was going out of sync with the real midsummer and midwinter dates. This was because the Julian calendar was ever so slightly too long. It was only a matter of minutes each year, but they added up.
By the fifteen hundreds it was getting noticeable to everybody that dates were wrong and this worried the Roman Catholic church who feared that celebrating important dates such as Easter at the wrong time might be considered an insult to God. In 1582 Pope Gregory introduced a change to the calendar that effectively moved everything back to roughly where the Church considered that it should be.
However the Eastern or Orthodox churches continued to follow the Julian calendar, and they do so to this day. This is why Eastern Orthodox Churches usually have differing Easter dates to Roman Catholic and Protestant Churches. We say usually, because in some years dates align themselves such that the whole world celebrates Easter on the same weekend.