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.
In actuality, the date of the Paschal Full Moon is determined from
historical tables, and has no correspondence to lunar events.
As Astronomers were able to approximate the dates of all the full
moons in future years, the Western Christian Church used these
calculations to establish a table of Ecclesiastical Full Moon dates.
These dates would determine the Holy Days on the Ecclesiastical
Though modified slightly from its original form, by 1583 AD the table
for determining the Ecclesiastical Full Moon dates was permanently
established and has been used ever since to determine the date of
Easter. Thus, according to the Ecclesiastical tables, the Paschal Full
Moon is the first Ecclesiastical Full Moon date after March 20 (which
happened to be the vernal equinox date in 325 AD). So, in Western
Christianity, Easter is always celebrated on the Sunday immediately
following the Paschal Full Moon.
The Paschal Full Moon can vary as much as two days from the date of
the actual full moon, with dates ranging from March 21 to April 18. As
a result, Easter dates can range from March 22 through April 25 in
Historically, western churches used the Gregorian Calendar to
calculate the date of Easter and Eastern Orthodox churches used the
Julian Calendar. This was partly why the dates were seldom the same.
Easter and its related holidays do not fall on a fixed date in either
the Gregorian or Julian calendars, making them movable holidays. The
dates, instead, are based on a lunar calendar very similar to the
While some Eastern Orthodox Churches not only maintain the date of
Easter based on the Julian Calendar which was in use during the First
Ecumenical Council of Nicea in 325 AD, they also use the actual,
astronomical full moon and the actual vernal equinox as observed along
the meridian of Jerusalem. This complicates the matter, due to the
inaccuracy of the Julian calendar, and the 13 days that have accrued
since 325 AD. This means, in order to stay in line with the originally
established (325 AD) vernal equinox, Orthodox Easter cannot be
celebrated before April 3 (present day Gregorian calendar), which was
March 21 in 325 AD.
Additionally, in keeping with the rule established by the First
Ecumenical Council of Nicea, the Eastern Orthodox Church adhered to
the tradition that Easter must always fall after the Jewish Passover,
since the death, burial and Resurrection of Christ happened after the
celebration of Passover. Eventually the Orthodox Church came up with
an alternative to calculating Easter based on the Gregorian calendar
and Passover, and developed a 19-year cycle, as opposed to the Western
Church 84-year cycle.
Since the days of early church history, determining the precise date
of Easter has been a matter for continued argument. For one, the
followers of Christ neglected to record the exact date of Jesus'
resurrection. From then on the matter grew increasingly complex.