Wikipedia:Date math 

Date math on Wikipedia is done with variables, templates, and the #time parser function. Here is a table which begins to list them:

Built-in variables Templates based on them What you see
{{UTC}} 2008-12-03 21:05 UTC
{{CURRENTDATE}} 21:05, Wednesday December 3 2008 (UTC)
{{CURRENTMONTH}} 12
{{CURRENTMNTH}} 12
{{User:Ed Poor/last month}} November
{{User:Ed Poor/this month}} December
{{User:Ed Poor/next month}} January
{{CURRENTDOW}} 3
{{User:Ed Poor/yesterday}} Tuesday
{{User:Ed Poor/today}} Wednesday
{{User:Ed Poor/tomorrow}} Thursday

Any variable or template with a resolution of smaller than one day should not placed in articles. These variables only indicate when the article was parsed and cached, they may be lagged by many hours or even days compared to the time the page is viewed.

Built-in variables Templates based on them What you see
{{CURRENTTIME}} 21:05
{{Current hour}} 21
{{Current minute}} 5

Fancy stuff

Today is
Tomorrow is

See also