Why Does The Date of Easter Change?

Three crosses in front of the moon

Christmas is always celebrated on the same date each year.. so why does the date of Easter always change?

This is a question that always comes up at this time of year as many people find it confusing. We all know that in the UK, the 25th December is always celebrated as Christmas Day, irrespective of whether it falls on a Sunday, Tuesday or whatever day of the week, and that never changes, (although it is a whole different date in The Canary Islands – but thats another story! ) So, why does the date that we celebrate Easter change every year?


There is quite a complicated explanation and alternate arguments for this, and you will probably find yourself a little confused when reading this and give up somewhere along the way. But, if you actually do want to know the answer, then read on. 

Easter Sunday always falls between March 22nd and April 25th ….. But Why?

In order to understand this, you first need to get to grips with the moon cycles, as irrespective of which religion or calendar you follow, that is where the original answer lies. 

EAST versus WEST

Historically Eastern Orthodox churches used the Julian calendar to calculate the dates for Easter, however, the Western churches use the Gregorian calendar. This is partly why the dates were seldom the same. Easter ,and its related days, do not fall on a fixed date each year, on either calendar, and are in fact more closely linked with the traditional Hebrew calendar, that was based on the cycles of the moon. 

The Paschal Moon

In the early years of the Christian church, the Sunday immediately following the astronomical full moon (the first moon after the Spring equinox) was considered the day to celebrate as Easter Sunday. Then in the year 325 AD, The First Ecumenical Council of Nicaea decided to adopt a more standardised system. Astronomers at that time were able to approximate the dates of all the future full moons, so they were calculated and the information compiled into a table. This table contained all the ecclesiastical full moon dates for the future, and enabled the church to work out the dates for Easter Sunday, well in advance. 

The Meridian Of Jerusalem

Many of the Eastern Orthodox churches still used the Julian calendar, thus complicating the matter further, as it was deemed inaccurate, because it did not coincide with the lunar cycles that could be seen along the meridian of Jerusalem. In addition, an extra thirteen days also accrued since 325 AD. So, in order to stay in line with the original table, in 1583 AD the table was modified accordingly. 

The Passover Moon

The Paschal moon can vary as much as two days from the date of the actual full moon, and the dates range from March 21st to April 18th. As a result, the dates for Easter in Western Christianity can also range from March 22nd to April 25th. If you work backwards,  April 3rd would have been the equivalent to March 21st (in 325 AD) which is why Orthodox Easter can never be celebrated before that date nowadays. In addition, The First Ecumenical Council of Nicaea also deemed that the resurrection of Christ happened after the Jewish celebration of Passover, a celebration which is also calculated by the Paschal (or Passover) moon. So, since then, the table that was created in 1583 AD, has been responsible for setting and decided the dates on which we celebrate Easter today, and is likely to continue to do so, well into the future.