Why Does Easter’s Date Change Every Year?

Easter—with its pastel colors and imagery of flowers, bunnies, and hatching chicks—is a sign that spring is here. For those who celebrate it for religious reasons, the holiday marks the resurrection of Jesus from the tomb in Christianity; those who enjoy it for secular reasons embrace the joy of eating rabbit-shaped chocolate and dyeing eggs. 

But when exactly Easter Sunday occurs during the season changes each year. In 2025, the holiday is April 20, which is one of the latest dates it can fall on. 

Why isn’t the date for Easter fixed in the same way as other Christian holidays? Christmas, for example, is always December 25, whereas the date of Easter can vary within a wide range of days in March and April under the standard calendar. The earliest it can be is March 22; its latest date possible is April 25. The holiday is what is known in religious terms as a moveable feast, meaning it can shift around the calendar, as opposed to a fixed feast like Christmas Day. 

Easter’s changing date is an issue that began long before the Gregorian calendar (named after Pope Gregory XIII) was instituted in 1582. (The Julian calendar—named for Julius Caesar—was the standard format for centuries before then.) Official formulations for working out Easter’s date were first established in 325 CE at what was known as the First Council of Nicaea in Ancient Rome; the council was held to try and reach agreement on a number of issues in the Christian church. 

The council determined that Easter should always be celebrated on the first Sunday following the full moon that occurs on or after the spring equinox. (The same council meeting also decided on December 25 as the date for Christmas.) The vernal equinox happens between March 19–21, depending on the year.

To make things more complicated, the full moon and spring equinox in question do not refer to the astrological ones. They instead follow ecclesiastical rules. According to these rules, an ecclesiastical full moon is always the 14th day of the ecclesiastical lunar month and the ecclesiastical equinox always falls on March 21. A complex formula that has evolved over the years is used to determine the date of future Easters (and someone even devised an algorithm that can help you find Easter dates for the years 1900–2099).

The calendar someone uses can change the date of Easter even more. Different branches of Christianity use different ones: Western churches use the Gregorian calendar, while the Eastern Orthodox Church continues to use the Julian calendar. Those within Catholic and Anglican churches, for example, may wind up celebrating the holiday on a different date than those in the Eastern Orthodox Church. But there are some years when the date of Easter in both the Gregorian and Julian calendars happens to fall on the same day—and such will be the case for 2025. 

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