The calculation of the date of Easter has a fascinating history, and algorithms and computer programs abound (for example, [1], [2], [9], [10], [13], and [14]). Many of the computations rely on the formulas of Gauss [5], [6] (see also [8]). Our fixed-date approach allows considerable simplification of “classical” algorithms.

The history of the establishment of the date of Easter is long and complex; good discussions can be found in [3] and [7]. The Council of Nicsa convened in 325 C.E. by Constantine the Great, was concerned with uniformity across various Christian groups. At the time of Nicæa, almost everyone in the official Church agreed to the definition that Easter was the first Sunday after the first full moon occurring on or after the vernal equinox [3] (a rule promulgated by Dionysius Exiguus and the Venerable Bede, who attributed it to the Council of Nicæa).