Time & Calendar
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Easter Date (Computus)

Core step of the Gregorian algorithm locating the Paschal full moon.

Formula

d=(19a+b) mod 30,a=y mod 19d = (19a + b) \bmod 30,\quad a = y \bmod 19

Variables

yYear
aGolden number − 1
dDays to Paschal moon

Example

Easter can fall anywhere from March 22 to April 25

Did You Know?

Computing Easter drove centuries of calendar mathematics — Gauss published his own Easter algorithm in 1800.

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