Why are Western and Orthodox Easter on different dates?

Western churches use the Gregorian calendar (reformed 1582) while the Eastern Orthodox church follows the Julian calendar. Both define Easter as the first Sunday after the first full moon on or after the spring equinox, but they use different calendars and different tables of ecclesiastical full moons.

What algorithm is used for Western Easter?

The Anonymous Gregorian algorithm (also called the Meeus/Jones/Butcher algorithm for the Gregorian calendar). It computes Easter Sunday for any year in the Gregorian calendar from 1583 onward without needing moon or equinox tables.

What algorithm is used for Orthodox Easter?

The Julian-calendar Easter algorithm (Meeus/Jones/Butcher for Julian), with the result converted to the Gregorian calendar by adding 13 days (valid for 1900–2099). This gives the Gregorian-calendar date on which Orthodox Easter falls.

Do they ever fall on the same date?

Yes, roughly 30% of years they coincide. When the Julian and Gregorian ecclesiastical full moons both point to the same Sunday, both traditions celebrate Easter on the same date.

Why does the range start at 1583?

The Gregorian calendar was adopted in October 1582. Western Easter dates before 1583 would use the Julian algorithm, which is outside the scope of this tool.

Easter Date Calculator

Name: Easter Date Calculator
Availability: InStock
Author: Nham Vu

Enter a year to instantly see both Western and Eastern Orthodox Easter dates.

Select a Year

Year (1583 – 2099)

Western Easter

Catholic & Protestant (Gregorian calendar)

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Orthodox Easter

Eastern Orthodox (Julian calendar, shown in Gregorian)

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Quick jump

Summary

Enter a year to instantly see both Western and Eastern Orthodox Easter dates.

How it works

Enter any year between 1583 and 2099 in the input field.
The calculator applies the Anonymous Gregorian algorithm to find Western Easter.
It applies the Julian-calendar algorithm (Meeus/Jones/Butcher) to find Orthodox Easter.
Both dates appear instantly, along with the number of days until each.
Use the arrow buttons or type directly to navigate between years.

Use cases

Plan travel or holidays around Easter weekend in advance.
Check if two Easter celebrations fall on the same date in a given year.
Satisfy curiosity about the historical formula determining Easter.
Coordinate events across Western and Eastern Christian traditions.
Look up Easter dates for any year for genealogy or historical research.

Frequently Asked Questions

Last updated: 2026-07-23 · Reviewed by Nham Vu