Computes the date of Western (Gregorian calendar) Easter Sunday for a given year using the Meeus/Jones/Butcher algorithm.
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Inputs
year (integer, required) min 1,583 : Gregorian calendar year (the algorithm is valid from 1583 onward, after the 1582 Gregorian reform)
Outputs
easter_date: ISO 8601 date of Western Easter Sunday
Steps
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.
m = floor((a + 11h + 22l) / 451).
month = floor((h + l - 7m + 114) / 31); day = ((h + l - 7m + 114) mod 31) + 1.
Constants
None.
Sources
Astronomical Algorithms, 2nd edition, chapter 8 (Easter) (Willmann-Bell (Jean Meeus), 2026-09-30T19:41:35Z) - the Meeus/Jones/Butcher algorithm for the Gregorian (Western) Easter date, valid from 1583 onward