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The Calendar of the Orthodox Church
By Lewis Patsavos, Ph.D.
Holy Cross School of Theology
© 1990-2000 Greek Orthodox Archdiocese of America

Within the Orthodox Church feast days and fast days are reckoned according
to two distinct calendars, the Julian Calendar and the Gregorian Calendar.
The first is attributed to the Roman Emperor Julius Caesar, whose name it
bears. It was later corrected in the sixteenth century by Pope Gregory XIII
due to the ever-increasing discrepancy between calendar time and calculated
astronomical time. Thus the Gregorian Calendar came into being.

Old and New Calendars

Inasmuch as the Julian Calendar had been in continuous use in the Christian
East and West throughout the centuries, the subsequent introduction of the
Gregorian Calendar in the West created yet another anomaly in the
deteriorating relations between the two Churches. The need for correction of
the Julian Calendar was well understood in the East and had even led some to
devise a new calendar themselves. Nevertheless, the Julian Calendar remained
in use throughout the Byzantine period and beyond. Despite the efforts of
the emissaries of Pope Gregory to convince the Orthodox to accept the New
(Gregorian) Calendar, the Orthodox Church rejected it. The main reason for
its rejection was that the celebration of Easter would be altered: contrary
to the injunctions of canon 7 of the Holy Apostles, the decree of the First
Ecumenical Synod, and canon 1 of Ancyra, Easter would sometimes coincide
with the Jewish Passover in the Gregorian calendar.

This is where the matter stood until the end of World War I. Until then, all
Orthodox Churches had strictly abided by the Old (Julian) Calendar, which at
present is 13 days behind the New Calendar long since adopted by the rest of
Christendom. In May of 1923, however, an "Inter­Orthodox Congress" was
convened at Constantinople by the then Ecumenical Patriarch, Meletios IV.
Not all Orthodox Churches were in attendance. The Churches of Serbia,
Romania, Greece, and Cyprus were; the Churches of Alexandria, Antioch and
Jerusalem, although invited, were not; the Church of Bulgaria was not
invited. Several issues were under discussion at the congress, one of which
was the adoption of the New Calendar. No unanimous agreement was reached on
any of the issues discussed. Several of the Orthodox Churches, however, did
eventually agree, though not all at the same time, to adopt the New
Calendar. These were the Churches of Constantinople, Alexandria, Antioch,
Greece, Cyprus, Romania, Poland, and most recently, Bulgaria (1968); on the
other hand, the Churches of Jerusalem, Russia and Serbia, along with the
monasteries on Mt. Athos, all continue to adhere to the Old Calendar.


The determination of the date of Easter is governed by a computation based
on the vernal equinox and the phase of the moon. According to the ruling of
the First Ecumenical Synod in 325, Easter Sunday should fall on the Sunday
which follows the first full moon after the vernal equinox. If the full moon
happens to fall on a Sunday, Easter is observed the following Sunday. The
day taken to be the invariable date of the vernal equinox is March 21.

Herein lies the first difference in the determination of Easter between the
Orthodox Church and the other Christian Churches. The Orthodox Church
continues to base its calculations for the date of Easter on the Julian
Calendar, which was in use at the time of the First Ecumenical Synod. As
such, it does not take into consideration the number of days which have
since then accrued due to the progressive inaccuracy of the Julian Calendar.
Practically speaking, this means that Easter may not be celebrated before
April 3 (Gregorian), which had been March 21--the date of the vernal
equinox--at the time of the First Ecumenical Synod. In other words, a
difference of 13 days exists between the accepted date for the vernal
equinox then and now. In the West, this discrepancy was addressed in the
16th century through the adoption of the Gregorian Calendar, which adjusted
the Julian Calendar still in use by all Christians at that time. Western
Christians, therefore, observe the date of the vernal equinox on March 21
according to the Gregorian Calendar.

The other difference in the determination of Easter between the Orthodox and
other Christian Churches concerns the date of Passover. Jews originally
celebrated Passover on the first full moon following the vernal equinox.
Christians, therefore, celebrated Easter on the first Sunday after the first
full moon following the vernal equinox. After the destruction of Jerusalem
in 70 A.D. and the other tragic events which gave rise to the dispersal of
the Jews, Passover sometimes preceded the vernal equinox. This was
occasioned by the dependence of the dispersed Jews upon local pagan
calendars for the calculation of Passover. As a consequence, most Christians
eventually ceased to regulate the observance of Easter by the Jewish
Passover. Their purpose, of course, was to preserve the original practice of
celebrating Easter following the vernal equinox.

As an alternative to calculating Easter by the Passover, "paschal (Easter)
cycles" were devised. The Orthodox Church eventually adopted a 19­year
cycle, the Western Church an 84-year cycle. The use of two different
"paschal cycles" inevitably gave way to differences between the Eastern and
Western Churches regarding the observance of Easter. Varying dates for the
vernal equinox increased these differences. Consequently, it is the
combination of these variables which accounts for the different date of
Orthodox Easter, whenever it varies from the rest of Christendom.


J. Dowden, The Church Year and Calendar. Cambridge, 1910.

D. R. Fotheringham, The Date of Easter and Other Christan Festivals. London,

K. T. Ware, The Orthodox Church. Penguin Books, 1982, pp. 304-310.