Zeller's congruence


Definition: An algorithm to find the day of the week for any date.

See also Doomsday rule.

Author: PEB


Dr J R Stockton's The Calendrical Works of Rektor Chr. Zeller: The Day-of-Week and Easter Formulae page has implementations of Zeller's congruence, for day-of-week (Pascal, JavaScript). The page includes tests and code for Easter, Zeller's original papers (and translations), etc. The following is only correct for Gregorian dates: Comp.lang.c FAQ question 17.28 (C).

More information

Wikipedia entry for Zeller's congruence. A summary of the International Standard Date and Time Notation ISO 8601.

Christian Zeller, Kalender-Formeln, Acta Mathematica, 9:131-6, Nov 1886.

Go to the Dictionary of Algorithms and Data Structures home page.

If you have suggestions, corrections, or comments, please get in touch with Paul Black.

Entry modified 14 September 2015.
HTML page formatted Fri Feb 23 10:06:08 2018.

Cite this as:
Paul E. Black, "Zeller's congruence", in Dictionary of Algorithms and Data Structures [online], Vreda Pieterse and Paul E. Black, eds. 14 September 2015. (accessed TODAY) Available from: