The Calendar FAQ includes a number of formulas for calculating various calendar values.

I have written a very simple implementation of these formulas in the C language. Rather than providing the most efficient code, the implementation intentionally follows the formulas very closely.

The code can be downloaded as a ZIP file

The photo below shows a tombstone located in the floor of the North Choir Aisle of Salisbury Cathedral in England. It illustrates how the new year hasn't always started on 1 January.

As described the Calendar FAQ, February had 30 days in Sweden in 1712.

The picture below shows two pages from a Swedish almanac from 1712.

You rarely get to see a 3-digit year in actual use. The photo below shows the date in a document signed by the Holy Roman Emperor Charles III (a.k.a. Charles the Fat) on 2 April 883.

Although a 30 February has indeed occurred in history, what about 31 February?

Translations of older versions of the Calendar FAQ are available in these languages:

• Belorussian (version 2.9)
• Russian (version 2.4)