Sometimes you are nice and early in the year on the Easter eggs, and sometimes you have to wait until well in April. This year, in 2025, Easter falls on April 20 and 21. But why does that date shift every year? And what does that mean for Ascension and Pentecost?
The date of Easter has everything to do with the moon. In 325 AD, the Council of Nicea (an important church meeting) agreed that Easter will be celebrated on the first Sunday after the first full moon in the spring.
This means that Easter always falls after March 21, because that is the fixed date before the beginning of spring according to the ecclesiastical calendar. Yet that does not mean that the full moon you see in the air is used. The church uses a fixed, mathematically certain lunar calendar, which sometimes deviates from the actual moon positions.
As a result, it may happen that the full moon that you see in the air does not always match the full moon that the ecclesiastical calculation is.
The earliest possible Easter date is March 22, if there is a full moon on March 21 (the first official spring day) and that falls on a Saturday. The last possible date is April 25, if the full moon only falls on April 18 and that is a Sunday (because then you have to wait another week for the following Sunday).
In 2025 the first full moon falls after the start of spring on April 13 (Sunday). That means that the next Sunday, April 20, is, and that is Easter Monday this year.
Easter also determines when Ascension and Pentecost falls: Ascension shipping is always 40 days after Easter, so on a Thursday. In 2025 that is on May 29. Pentecost comes 10 days after Ascension, or 50 days after Easter. This falls in 2025 on 8 and 9 June.
This calculation method has been used for centuries and is part of the traditional ecclesiastical calendar. The reason Easter does not just have a fixed date, such as Christmas (December 25), is because the party is originally to do with the Jewish Passover party. That is also determined by the lunar calendar and usually falls around the same time as Easter.
Not everywhere in the world people celebrate Easter on the same day. The Eastern Orthodox churches use the Julian calendar instead of the Gregorian calendar that we use.
As a result, Orthodox Easter often falls on a different date than our Easter. In 2025, for example, the Orthodox Churches Easter on 27 April, a week later than we are. This difference arises because the Julian calendar has been lagging behind the Gregorian calendar for 13 days.
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