Claus Tøndering –
(Please include the word “calendar” in the subject line)

Frequently Asked Questions about Calendars

Since March 1996 I have had the pleasure to edit the “Calendar FAQ.” This has been a source of great enjoyment both for me and – I hope – for my readers.

Please enjoy this Calendar FAQ. You will find the table of contents in the left hand column.

Best wishes,
Claus Tøndering, Kongens Lyngby, Denmark

Writing dates

Throughout these pages, dates will be written in the British format (1 January) rather than the American format (January 1). Dates will occasionally be abbreviated: “1 Jan” rather than “1 January”.

Years before and after the “official” birth year of Christ will be written “45 BC” or “AD 1997”, respectively. I prefer this notation over the secular “45 BCE” and “1997 CE”.


A simple C language implementation of all the formulas given in this document can be found at Calendar Algorithms.

Copyright and disclaimer

This document is Copyright ©2021 by Claus Tøndering.

The document may be freely distributed, provided this copyright notice is included and no money is charged for the document.

This document is provided “as is”. No warranties are made as to its correctness.