easter

How the date of Easter is determined

Easter is what the Church calls a “movable feast,” meaning its date changes each year based on a defined rule rather than a fixed calendar day. In Western Christianity, the rule is as follows: Easter is celebrated on the first Sunday after the first full moon that occurs on or after March 21, which is treated as the spring equinox for ecclesiastical purposes.

There are two key technical details in that rule. First, the “full moon” used is not the exact astronomical full moon observed in the sky, but an ecclesiastical full moon calculated using standardized lunar tables developed by the Church. This ensures consistency across regions and centuries. Second, the equinox is fixed to March 21 in the Church’s system, even though the actual astronomical equinox can fall on March 19, 20 or 21.

The calculation works in sequence. Once March 21 is reached, the Church identifies the next calculated full moon, known as the Paschal Full Moon. Easter is then set as the first Sunday after that full moon. If the full moon falls on a Sunday, Easter is observed the following Sunday.

This system ties Easter to both the solar year, through the equinox, and the lunar cycle, through the full moon. That hybrid structure reflects the historical context of the holiday.

Easter commemorates the resurrection of Jesus Christ, which, according to the New Testament, took place shortly after the Jewish festival of Passover. Passover is determined using the Hebrew calendar, which is based on lunar cycles. Early Christians linked the timing of Jesus’ crucifixion and resurrection to Passover, and therefore to the full moon.

However, early Christian communities did not all follow the same method for determining the date, leading to disagreements. To establish uniformity, church leaders formalized the current approach at the First Council of Nicaea in 325 AD. The intent was to ensure that all Christians celebrated Easter on the same day while maintaining its connection to Passover and its seasonal symbolism.

Because of the interaction between a fixed equinox date, a calculated lunar cycle and the requirement that Easter always fall on a Sunday, the holiday can occur only between March 22 and April 25.

A note on modern observance

In contemporary culture, Easter is often associated with symbols such as bunnies, eggs and candy, with little or no reference to Jesus Christ or the religious meaning of the day. While some of these symbols have historical roots in themes like new life and spring, they can obscure the original purpose of the holiday.

The dating of Easter was never arbitrary. It was carefully structured to align with the timing of Passover and to commemorate what Christians believe is the central event of the faith: the resurrection of Jesus. The concept of a movable feast exists specifically to preserve that connection.

Remembering how and why the date is set provides context that is often missing in modern celebrations. The calendar rule is not just a curiosity. It reflects a deliberate effort by the early Church to anchor the observance in both history and theology.

Sources

• Encyclopaedia Britannica, “Easter holiday”
  
  https://www.britannica.com/topic/Easter-holiday

• U.S. Naval Observatory, “Date of Easter”
  
  https://aa.usno.navy.mil/faq/easter

• Catholic Encyclopedia, “Easter”
  
  https://www.newadvent.org/cathen/05224d.htm

• BBC, “Why does the date of Easter change?”
  
  https://www.bbc.co.uk/newsround/60959500

• The Book of Common Prayer (Episcopal Church), “Tables and Rules for the Movable and Immovable Feasts”
  
  https://www.bcponline.org/General/tables.html