Why does the date for Easter change every year? Have you ever wondered why Easter Sunday can fall anywhere between March 22 and April 25? And why do Eastern Orthodox churches celebrate Easter on a different day than Western churches? These are all good questions with answers that require a bit of explanation. In fact, there are as many misunderstandings about the calculation of Easter dates, as there are reasons for the confusion. What follows is an attempt to clear up at least some of the confusion.
In Western Christianity, Easter is always celebrated on the Sunday immediately following the Paschal Full Moon date of the year. I had previously, and somewhat erroneously stated, "Easter is always celebrated on the Sunday immediately following the first full moon after the vernal (spring) equinox." This statement was true prior to 325 AD; however, over the course of history (beginning in 325 AD with the Council of Nicea), the Western Church decided to established a more standardized system for determining the date of Easter.