Calculating the date of Easter

http://www.whydomath.org/Reading_Room_Material/ian_stewart/2000_03.html

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Choose any year of the Gregorian calendar and call it x. To determine the date of Easter, carry out the following 10 calculations (it’s easy to program them on a computer):

1. Divide x by 19 to get a quotient (which we ignore) and a remainder A. This is the year’s position in the 19-year lunar cycle. (A + 1 is the year’s Golden Number.)

2. Divide x by 100 to get a quotient B and a remainder C.

3. Divide B by 4 to get a quotient D and a remainder E.

4. Divide 8B + 13 by 25 to get a quotient G and a remainder (which we ignore).

5. Divide 19A + B – D – G + 15 by 30 to get a quotient (which we ignore) and a remainder H.
(The year’s Epact is 23 – H when H is less than 24 and 53 – H otherwise.)

6. Divide A + 11H by 319 to get a quotient M and a remainder (which we ignore).

7. Divide C by 4 to get a quotient J and a remainder K.

8. Divide 2E + 2J – K – H + M + 32 by 7 to get a quotient (which we ignore) and a remainder L.

9. Divide H – M + L + 90 by 25 to get a quotient N and a remainder (which we ignore).

10. Divide H – M + L + N + 19 by 32 to get a quotient (which we ignore) and a remainder P.

Easter Sunday is the Pth day of the Nth month (N can be either 3 for March or 4 for April).
The year’s dominical letter can be found by dividing 2E + 2J – K by 7 and taking the remainder (a remainder of 0 is equivalent to the letter A, 1 is equivalent to B, and so on).