Dates

In dates, set off the year with a pair of commas.

exceptions: Commas are not needed if the date is inverted or if only the month and year are given: 15 April 2009; January 2008.

Addresses

The elements of an address or a place name are separated with commas. A zip code, however, is not preceded by a comma.

Titles

If a title follows a name, set off the title with a pair of commas.

Numbers

In numbers more than four digits long, use commas to separate the numbers into groups of three, starting from the right. In numbers four digits long, a comma is optional.

3,500 [or 3500] 100,000 5,000,000

exceptions: Do not use commas in street numbers, zip codes, telephone numbers, or years with four or fewer digits.