Wikipedia:Date math

Date math on Wikipedia is done with variables, templates and the  parser function.

In articles, it is almost always preferred to specify a specific static date for a statement or event rather than an automatically generated date. As of describes how to properly specify such dates.

Computed date and time
Julian dates or day numbers can be used for date calculations. A simple example follows:
 * 1) 90 days from 25 December 2006 is: 
 * 2) * Code:
 * 3) 90 days from 25 December 2007 is:  (1 day less than first example due to leap year in 2008)
 * 4) * Code: