/// /// Algorithm for calculating the date of Easter Sunday /// (Meeus/Jones/Butcher Gregorian algorithm) /// http://en.wikipedia.org/wiki/Computus#Meeus.2FJones.2FButcher_Gregorian_algorithm /// /// A valid Gregorian year /// Easter Sunday public static DateTime EasterDate(int year) { int Y = year; int a = Y % 19; int b = Y / 100; int c = Y % 100; int d = b / 4; int e = b % 4; int f = (b + 8) / 25; int g = (b - f + 1) / 3; int h = (19 * a + b - d - g + 15) % 30; int i = c / 4; int k = c % 4; int L = (32 + 2 * e + 2 * i - h - k) % 7; int m = (a + 11 * h + 22 * L) / 451; int month = (h + L - 7 * m + 114) / 31; int day = ((h + L - 7 * m + 114) % 31) + 1; DateTime dt = new DateTime(year, month, day); return dt; } Easter Monday = Easter Sunday + 1 Ascension Day = Easter Sunday + 39 Pentecost Sunday = Easter Sunday + 49 Pentecost Monday = Easter Sunday + 50