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. Links to the full ISO 8601:2004 standard (or use this link then click ISO Standard 8601 if the above gets page not found).

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 3 December 2012.
HTML page formatted Mon Feb 2 13:10:40 2015.

Cite this as:
Paul E. Black, "Zeller's congruence", in Dictionary of Algorithms and Data Structures [online], Vreda Pieterse and Paul E. Black, eds. 3 December 2012. (accessed TODAY) Available from: