Determination of the Day of the Week

Determination of the day of the week covers the family of algorithms used to calculate what day of the week any given calendar date falls on. Most methods start from a known anchor date, such as 1 January 1800 being a Wednesday, count the number of days to the target date, and reduce that count modulo seven. Named approaches in this family include Gauss's algorithm, Zeller's congruence, Wang's method and the Doomsday rule, alongside tabular lookup methods and historical techniques such as Lewis Carroll's. These methods are used both for mental calculation and in computer programs, and are adapted to work for the Julian and Gregorian calendars, commonly to find the weekday of a birth or historical event. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/