When a date is written traditionally as month-day-year, a comma should be placed between the day and the year. For example:
- July 4, 1776
When a traditionally-written date is inserted into a sentence, an addition comma should be inserted after the year. For example:
- On July 4, 1776, the United States declared its independence.
Alternatively, these dates can be written in the British style (also common in other countries and the US Army):
- The United States declared its independence on 4 July 1776.
When the day of the week is added, put a comma between it and the rest of the date. For example:
- On Tuesday, March 16, we will be going on a field trip to the National Museum of Art.
Always insert a comma between a city and state. In a sentence, insert a comma after the state as well. For example:
- Last year, we traveled to Cincinnati, Ohio, for a three-day conference.
When you are writing a complete address in sentence form, separate all elements of the address except for the zip code and the element that precedes it. For example:
- Myra addressed the envelope to Sally Rosen, 43 Open House Ave., Baltimore, MD 21209, and sealed it shut.
When writing numbers or prices that are more than four digits, insert a comma after every three digits from the right. Some style guides require a comma for a four-digit numbers as well. (This does not apply to zip codes, page numbers, or most dates.) For example:
- The house cost $240,000.
- There were 35,000 people at the rally.
If a name is followed by an academic degree, the name should be separated from the title with a comma. If additional words follow the degree, the degree should be followed by a comma as well. For example:
- Paula Wanger, PhD, will be speaking at the conference tonight.
Although some style guides specify differently, most people do not include a comma between a name and a suffix. For example:
- Martin Luther King Jr. is one of the most famous supporters of human rights.
- Richard III became king of England in 1483.
This post is part of the series: When to Use Commas: A List of Comma Rules
Confused by commas? These rules for comma usage will teach you how and when to use commas. Includes information about items in a series, introductory phrases, and comma splices.