Carter's Method:
Valid 1900-2099 ONLY

This page was last updated 1999 January 21 by M.J. Montes.
This is an excerpt from the Royal Greenwich Observatory's Leaflet on the Date of Easter:

An algorithm to find the date of Easter which is valid from 1900 to 2099 has been derived by Carter. (Below: Y MOD 19 is the integer reminder of Y/19. [Y/4] is the integer part of Y/4. )

  1. Calculate B = 225 - 11(Y MOD 19).
  2. Calculate D = ((B-21) MOD 30) + 21.
  3. If D is greater than 48 subtract 1 from it.
  4. Calculate E = (Y + [Y/4] + D + 1) MOD 7 .
  5. Calculate Q= D + 7 - E.
  6. If Q is less than 32 then Easter is in March (on the Qth day). If Q is greater than 31 then Q - 31 is its date in April.

See also Oudin's algorithm, and Butcher's Algorithm, other algorithms for determining Easter in the Western Church, and Gauss' algorithm which is used by the Orthodox Church.
Calculation of the Ecclesiastical Calendar


Last updated 1999 January 21.
Thanks to James Holdcroft for simplifying the second step.
Marcos Montes
mmontes@nospam.smart.net