How Is the Date of Easter Calculated?

Easter is a moveable feast, which means that it does not occur on the same date every year.

The Council of Nicaea (A.D. 325) set the date of Easter as the Sunday following the paschal full moon, which is the full moon that falls on or after the vernal (spring) equinox.

The reason being is that the paschal full moon is the date of Passover in the Jewish calendar, and the Last Supper (Holy Thursday) occurred on the Passover. Christ was crucified on the Friday and was resurrected on the Sunday. Therefore, Easter is the Sunday after Passover.

The Church does not use the exact date of the paschal full moon but an approximation, because the paschal full moon can fall on different days in different time zones, which would mean that the date of Easter would be different depending on which time zone you live in.

Easter Dates

' Given the Year as a four digit number in the range 1700 - 2299
' Calculate Day and Month of Easter Sunday
' Note 1: the \ operator performs integer division without remainder.
' Note 2: the date returned is the Gregorian Calendar date
'         (the one we use now), even for dates in the 18th Century.

a = Year mod 19;
b = Year \ 100;
c = Year mod 100;
d = b \ 4;
e = b mod 4;
f = c \ 4;
g = c mod 4;

h = (b + 8)\25;
i = (b - h + 1)\3;
j = (19*a + b - d - i + 15) mod 30;
k = (32 + 2*e + 2*f - j - g) mod 7;
m = (a + 11*j + 22*k) \ 451;
n = j + k - 7*m + 114;

Month = n\31;
Day = (n mod 31) + 1;