Traditions · Explainer

Why Eastern & Western Easter Dates Differ

Easter is a moveable feast — and it moves differently for Eastern Orthodox and Western Christian churches. The gap comes down to two calendars, a 4th-century council, and 13 drifting days. When the dates diverge, so does Pancake Day.

In brief

Both Eastern and Western churches follow the Council of Nicaea rule (325 AD): Easter is the first Sunday after the first full moon after the spring equinox. The difference is which calendar they use to find that equinox. Western churches use the Gregorian calendar (1582). Most Orthodox churches use the Julian calendar — which today runs 13 days behind the Gregorian. This shifts their “spring equinox” to April 3 in Gregorian terms, potentially pushing Orthodox Easter up to five weeks later than Western Easter.

The Council of Nicaea and the Easter formula

In 325 AD, the Council of Nicaea — the first ecumenical council of the Christian Church — established the method for calculating Easter. The formula, called the computus, states: Easter is the first Sunday after the first ecclesiastical full moon that falls on or after March 21 (the spring equinox).

The Council also ruled that Easter should not coincide with the Jewish Passover, and that it should be observed on the same day by all Christians worldwide. This last ambition did not survive the next twelve centuries intact.

The Nicaea formula uses “ecclesiastical” full moons — tabulated dates calculated by a fixed cycle rather than actual astronomical observation. This is why Easter is sometimes a day or two off from the actual full moon. Both Western and Eastern churches use ecclesiastical rather than astronomical full moons, but they use different tables.

Julian vs Gregorian: the 13-day drift

The Julian calendar — established by Julius Caesar in 46 BC — adds a leap day every four years without exception, giving an average year of 365.25 days. The actual solar year is 365.2422 days, so the Julian calendar gains roughly one day every 128 years.

By the 16th century, the accumulation of this error had shifted the calendar 10 days relative to the sun. Pope Gregory XIII introduced the Gregorian reform in 1582: 10 days were dropped from October 1582 (October 4 was followed by October 15), and the leap year rule was refined — century years (1700, 1800, 1900, 2100…) are not leap years unless divisible by 400. This keeps the calendar aligned with the solar year to within 1 day per 3,300 years.

Western European Catholic countries adopted the Gregorian calendar immediately. Protestant countries followed over the next century and a half (Britain in 1752). Eastern Orthodox churches, politically and institutionally separate from Rome, declined to adopt the Gregorian reform and continued using the Julian calendar.

Since 1582, the Julian calendar has drifted a further 3 days behind the Gregorian (the century years 1700, 1800, and 1900 were Julian leap years but Gregorian non-leap years). Today the Julian calendar runs 13 days behind the Gregorian. Julian March 21 is Gregorian April 3.

Comparison: Western vs Eastern Easter calculation

	Western	Eastern Orthodox
Calendar used	Gregorian (since 1582)	Julian (pre-1582, unchanged)
Calendar gap today	—	Julian runs 13 days behind Gregorian
Spring equinox	March 20–21 (astronomical)	April 3 (Julian March 21 = Gregorian April 3)
Full moon used	Ecclesiastical (tabular)	Ecclesiastical (different tables)
Max date gap	—	Up to 5 weeks after Western Easter
Dates coincide	Roughly 1 in 4–5 years	Same
Shrove Tuesday	47 days before Easter	47 days before Orthodox Easter

What this means for Shrove Tuesday in Orthodox countries

Shrove Tuesday — the day before Ash Wednesday — is always 47 days before Easter Sunday. In Orthodox countries, it is 47 days before Orthodox Easter.

When Eastern and Western Easter coincide (roughly one year in four), Shrove Tuesday in Russia, Greece, Serbia, Romania, and Bulgaria falls on the same date as Pancake Day in England and Mardi Gras in New Orleans. When they diverge — up to five weeks apart — the Orthodox Shrovetide season happens significantly later.

In Russia, the pre-Lenten week is called Maslenitsa — a seven-day festival that includes pancake eating (blini with butter, sour cream, and caviar), the burning of a straw winter effigy, and outdoor festivities. Because it follows the Orthodox calendar, Maslenitsa can occur weeks after Western Shrove Tuesday. Greeks celebrate Apókries (the equivalent of Carnival) for three weeks leading up to Orthodox Ash Monday.

The same offset applies to all Orthodox-majority countries: Serbia (Poklade), Bulgaria, Romania, Ethiopia (which uses its own Ge'ez calendar, diverging further still), and the Coptic Church.

Frequently Asked Questions

Why do Orthodox and Western Easter fall on different dates?+

The difference comes down to two different calendars used to calculate Easter. Western churches (Catholic, Protestant, Anglican) use the Gregorian calendar, introduced in 1582. Most Eastern Orthodox churches use the older Julian calendar, which runs 13 days behind the Gregorian calendar today. Since Easter is calculated relative to the spring equinox and a full moon, and the two calendars place the equinox on different dates, the calculated Easter date diverges — sometimes significantly. In some years the dates coincide; in others they are up to five weeks apart.

What did the Council of Nicaea decide about Easter?+

The Council of Nicaea in 325 AD established that Easter should be celebrated on the first Sunday after the first full moon on or after the spring equinox — and that it should not coincide with the Jewish Passover. This formula, called the "computus," was designed to unify Easter observance across the Christian world. However, the Council did not specify which calendar to use, and the Julian calendar was the only option at the time. When the Gregorian reform came in 1582, Eastern churches declined to adopt it, maintaining the Julian reckoning — and the divergence began.

What is the difference between the Julian and Gregorian calendars?+

The Julian calendar, established by Julius Caesar in 46 BC, adds a leap day every four years — giving an average year of 365.25 days. The actual solar year is 365.2422 days, so the Julian calendar gains roughly 1 day every 128 years relative to the sun. By the 16th century, the Julian calendar was 10 days ahead of the actual solar year. Pope Gregory XIII's reform (1582) corrected this by dropping 10 days and refining the leap year rule: century years are not leap years unless divisible by 400. Today the Julian calendar is 13 days behind the Gregorian.

When does Eastern Easter coincide with Western Easter?+

Eastern and Western Easter fall on the same date in roughly one year out of every four to five. This happens when the full moon used to calculate Easter falls on a date where both the Julian and Gregorian reckoning point to the same Sunday. They coincided in 2025 and will coincide again in 2028, 2031, and 2034. When they coincide, Shrove Tuesday falls on the same date in Orthodox and Western countries.

What is the Orthodox Shrove Tuesday (Maslenitsa)?+

In Russian Orthodox tradition, the equivalent of Shrove Week is Maslenitsa (Масленица) — a week-long festival preceding the Great Lent. Maslenitsa has strong pre-Christian elements: it involves burning an effigy of winter (Maslenitsa doll), communal feasting on blini (thin pancakes with butter and sour cream), and public festivities. Because Orthodox Easter is calculated on the Julian calendar, Maslenitsa can fall anywhere from the same week as Western Shrove Tuesday to five weeks later. Other Orthodox countries (Greece, Serbia, Romania, Bulgaria) have their own equivalent pre-Lenten festivals, all subject to the same calendar offset.

Will Eastern and Western Easter ever be permanently unified?+

This remains a live question in ecumenical discussions. The World Council of Churches proposed in 1997 that all Christian churches fix Easter to the second or third Sunday in April, using an astronomical calculation rather than either the Julian or Gregorian calendar formula. This proposal has not been adopted by any major church body. The Catholic Church has indicated openness to reform if Orthodox churches agree; most Orthodox churches have resisted change. For now, the divergence persists.

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