commas in a date

Use a comma to separate the day of the week from the date and the day from the year:

• Friday, February 13 (but Friday the thirteenth)
• Monday, October 26, 2015

When the date appears in a sentence in the sequence month-day-year, a comma is needed after the year as well as before it (except when the comma is replaced by a stronger mark of punctuation):

• He worked in my department from May 20, 2001, until October 28, 2003, when he accepted another assignment.
• We planned to finish the project by January 8, 2009; however, we completed the work on December 15, 2008.

But when the day is omitted, there is no comma either before or after the year:

• He worked in my department from May 2001 until October 2004.
• The Esplanade Riel pedestrian bridge opened in December 2003.

When the date is written in the sequence day-month-year (a style more common outside of North America), commas are not used:

• He worked in my department from 20 May 2001 until 28 October 2003.