Tech Friday: How Is The Date of Easter Determined?
Posted By RichC on March 21, 2025
Have you ever wondered how the yearly floating date for Easter is determined … or why it is so late this year (April 20, 2025)?
Almanac.com had a great article, but since I’m thinking about Tech Friday today, here’s what Grok3 AI has to say about it. 
The date of Easter Sunday is determined by a system rooted in both lunar and solar cycles, specifically tied to the Paschal Full Moon. The Paschal Full Moon is the first full moon that occurs on or after the ecclesiastical spring equinox, which the Christian Church fixes as March 21 for simplicity, even though the astronomical equinox can vary slightly (e.g., in 2025, it’s March 20). Easter Sunday is then set as the first Sunday following this Paschal Full Moon.
This method connects Easter to the Jewish calendar, where lunar cycles (approximately 29.5 days) govern key dates like Passover. In Christianity, Easter commemorates the resurrection of Jesus, which followed the Last Supper—a Passover feast. Because it’s tied to the lunar month rather than a fixed solar date like Christmas (December 25, near the winter solstice), Easter’s date shifts each year. For example, if the Paschal Full Moon falls on a Saturday, Easter is the next day; if it’s a Monday, Easter is the following Sunday.
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