How is the date of Easter determined each year?

Easter is a "moveable feast," meaning its date changes annually; it is determined by the first Sunday following the Paschal Full Moon—the first full moon occurring on or after March 21, which represents the ecclesiastical spring equinox ([Time and Date](https://www.timeanddate.com/calendar/determining-easter-date.html)). This complex calculation, historically known as *computus paschalis*, ensures that the holiday remains tied to the lunar cycle and the spring season, illustrating the ancient intersection of astronomy, religious tradition, and calendar systems that continues to influence modern scheduling.

### Why does Easter fall on a different date every year?
Unlike holidays such as Christmas, which are fixed to a solar calendar date, Easter’s date is dictated by a lunisolar system. Because the lunar cycle (approximately 29.5 days) does not align perfectly with the solar year, the Paschal Full Moon moves through the calendar, creating a window for Easter Sunday that can occur anytime between March 22 and April 25 ([Grace Church](https://gracechurch.us/articles/what-determines-the-date-of-easter)). This variability was established by the Council of Nicaea in 325 AD, which sought to standardize the celebration of Easter independently of the Jewish calendar, while maintaining the connection to the lunar-based timing of Passover ([Catholic Answers](https://www.catholic.com/qa/how-is-easter-sunday-determined-palm-sunday-ash-wednesday)).

### Is the date of Easter the same for all Christian churches?
Not necessarily. While most Western churches, including the Roman Catholic Church and many Protestant denominations, follow the Gregorian calendar to calculate the date, many Orthodox churches continue to use the older Julian calendar for their liturgical calculations ([World Council of Churches](https://www.oikoumene.org/resources/documents/frequently-asked-questions-about-the-date-of-easter)). Because the Julian calendar currently runs 13 days behind the Gregorian calendar, the Orthodox celebration of Easter often falls on a different date than Western Easter, though they occasionally coincide when the lunar cycles align across both calendar systems.

### How are other related religious dates calculated?
The date of Easter serves as the anchor for the entire liturgical calendar. Once Easter Sunday is fixed, the dates for other significant observances are derived by counting backward or forward from that day ([Catholic Answers](https://www.catholic.com/qa/how-is-easter-sunday-determined-palm-sunday-ash-wednesday)). For example, Ash Wednesday is calculated by counting 46 days prior to Easter, while Palm Sunday is established as the Sunday immediately preceding Easter. This interconnected calendar structure highlights how the variability of Easter ripples through the entire Christian liturgical year.

### Key Takeaways
* **Moveable Feast:** Easter is not tied to a fixed date but to the cycle of the moon and the spring equinox.
* **The Rule:** Easter always falls on the first Sunday after the first full moon on or after March 21.
* **Calendar Differences:** Variations exist between Western (Gregorian) and Orthodox (Julian) calculations, leading to different observation dates.
* **Calendar Anchor:** Easter determines the timing of many other religious events, including Lent and Palm Sunday.

Understanding the complexity of how Easter is calculated provides insight into the historical attempt to harmonize astronomical reality with religious observance. While the "moveable" nature of the holiday may seem unpredictable in a modern, efficiency-driven world, it preserves a tradition that is thousands of years old. As technology continues to evolve, the adherence to these traditional calculations remains a testament to the influence of ancient celestial observations on contemporary global culture.

## References
* [Catholic Answers: How are the dates for Easter, Palm Sunday, and Ash Wednesday determined?](https://www.catholic.com/qa/how-is-easter-sunday-determined-palm-sunday-ash-wednesday)
* [Grace Church: What determines the date of Easter?](https://gracechurch.us/articles/what-determines-the-date-of-easter)
* [Time and Date: How Is Easter Determined?](https://www.timeanddate.com/calendar/determining-easter-date.html)
* [Wikipedia: Date of Easter](https://en.wikipedia.org/wiki/Date_of_Easter)
* [World Council of Churches: Frequently asked questions about the date of Easter](https://www.oikoumene.org/resources/documents/frequently-asked-questions-about-the-date-of-easter)