How this calculator works
The rule set by the Council of Nicaea ties Easter to the ecclesiastical full moon, which follows a repeating 19 year cycle rather than the true moon. Easter is the first Sunday after that full moon, and the computus also adjusts for the difference between the Julian and Gregorian calendars. The result falls between 22 March and 25 April, so the date moves by up to five weeks from year to year. The other movable feasts count from Easter: Ash Wednesday is 46 days before, Good Friday two days before, and Pentecost 49 days after. Fixed feasts such as Christmas do not move.
Formula
Use the Gregorian computus: with a = year mod 19, b = floor(year / 100), c = year mod 100, d = floor(b / 4), e = b mod 4, f = floor((b + 8) / 25), g = floor((b - f + 1) / 3), h = (19a + b - d - g + 15) mod 30, i = floor(c / 4), k = c mod 4, l = (32 + 2e + 2i - h - k) mod 7 and m = floor((a + 11h + 22l) / 451). Then month = floor((h + l - 7m + 114) / 31) and day = ((h + l - 7m + 114) mod 31) + 1.
Worked example
For 2024 the computus gives 31 March, so Ash Wednesday is 14 February, Palm Sunday is 24 March, Good Friday is 29 March and Easter Monday is 1 April. Ascension Day is 9 May, Pentecost is 19 May and Corpus Christi is 30 May. For 2025 Easter falls on 20 April, for 2026 on 5 April and for 2027 on 28 March. The earliest possible date, 22 March, last occurred in 1818 and next occurs in 2285; the latest, 25 April, occurs in 2038.
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Frequently asked questions
Why does the date of Easter change every year?
Easter follows the moon rather than the sun. It is tied to the first ecclesiastical full moon after the spring equinox, so the date shifts through a range of about a month as the lunar cycle moves against the calendar.
Why do some churches celebrate on a different day?
Orthodox churches that use the Julian calendar for the computus often celebrate later than Western churches, and some calculate the equinox differently. The gap can be one, four or five weeks depending on the year.
What is the earliest and latest Easter?
In the Gregorian calendar Easter can fall from 22 March to 25 April. 2285 gives 22 March and 2038 gives 25 April, which are useful reference years when checking a computus.
Are these dates the same worldwide?
The dates are calendar dates in the Gregorian calendar. Observance times differ by time zone, and local public holidays may move to the nearest Monday, but the underlying feast dates are the same.