Ask two Orthodox families when Saint Nicholas' day is, and you may get two answers — December 6 and December 19. Both are right. The Orthodox world lives on two calendars, and understanding why is simpler than it looks.
The Julian calendar and its slow drift
The Julian calendar, introduced under Julius Caesar in 45 BC, assumes a year of exactly 365.25 days. The true solar year is about eleven minutes shorter. Eleven minutes sounds like nothing, but over centuries it adds up to about one day every 128 years. By the sixteenth century the calendar had slipped roughly ten days out of step with the seasons; today the gap is thirteen days, and it will grow to fourteen in the year 2100.
The West corrected the drift in 1582 with the Gregorian calendar of Pope Gregory XIII, which trims three leap days every four hundred years. The Orthodox Church, for whom the calendar was woven into a shared liturgical life, did not adopt the papal reform.
1923: the Revised Julian calendar
In 1923, a congress in Constantinople proposed the Revised Julian calendar — a correction that is astronomically even slightly more accurate than the Gregorian, and identical to it in practice until the year 2800. Churches that adopted it moved their fixed feasts (Christmas, Theophany, the saints' days) into line with civil dates. These are the “New Calendar” churches. Churches that kept the unreformed Julian reckoning are the “Old Calendar” churches — their fixed feasts fall thirteen civil days later.
That is the whole mystery of “Orthodox Christmas on January 7”: Old Calendar churches celebrate the Nativity on December 25 of the Julian calendar, which currently lands on January 7 of the civil calendar. Nobody moved Christmas; the calendars moved around it.
Who follows which calendar?
| New (Revised Julian) | Old (Julian) |
|---|---|
| Ecumenical Patriarchate of Constantinople, Alexandria, Antioch, Greece, Cyprus, Romania, Bulgaria, Albania, and most of the Orthodox Church in America | Russia, Serbia, Georgia, Jerusalem, the monasteries of Mount Athos, and parts of the Orthodox world in Ukraine and elsewhere |
The picture continues to shift: much of the Orthodox Church of Ukraine adopted the New Calendar for fixed feasts in 2023. Diaspora parishes add another layer — a Greek parish and a Serbian parish in the same city may keep the same feast thirteen days apart, and mixed families quietly keep both.
The crucial exception: Pascha
Here is the point most often missed: nearly all Orthodox churches — Old and New Calendar alike — celebrate Pascha on the same day, because the paschal reckoning was left on the Julian system even by New Calendar churches (the Church of Finland is the rare exception). So an Orthodox family in Athens and one in Moscow will differ about Christmas but stand together at the same midnight Paschal Liturgy. How that date is computed is a story of its own — see When Is Orthodox Easter?
What this means in daily life
- Your name day depends on your church's calendar: Saint Nicholas is December 6 for New Calendar families, December 19 (civil) for Old Calendar families. (More in What Is a Name Day?)
- Fixed feasts and fasts shift the same way: the Nativity Fast begins November 15 on the New Calendar, November 28 (civil) on the Old.
- If your parish, your in-laws, and your godparents span both calendars, you effectively need two calendars at once — which is exactly why a one-tap switch matters.
How the Orthodox Calendar app helps
Orthodox Calendar switches between the Julian (Old) and Revised Julian (New) calendars with one tap. Saints, name days and the month view all follow the calendar you choose, so a family that keeps both never has to do the thirteen-day arithmetic in their heads.
Related guides
- When Is Orthodox Easter? How the Date of Pascha Is Calculated
How the date of Orthodox Easter (Pascha) is calculated, why it usually differs from Western Easter, and upcoming dates: April 12, 2026 and May 2, 2027.
- Feast Days of the Orthodox Church: Pascha, the Twelve Great Feasts, and the Ranks of Saints
The feast days of the Orthodox Church: Pascha, the Twelve Great Feasts with their dates, and the ranks of saints — Apostle, Martyr, Venerable, and more.
- Whose Greek Name Day Is It Today?
How to find today's Greek Orthodox name day, how names map to saints, major name days through the year, and an app that checks your contacts for you.
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