Comma after Abbreviation (When Period Ends an Abbreviation)

While placing a comma after a period might look weird, it is sometimes a necessity. You need to know when it is correct to do this, and it all comes down to whether you’re using abbreviations. This article will explain when to place a comma after an abbreviation.

Comma after Abbreviation?

You should place a comma after an abbreviation when it is part of a list, introductory clause, or a comma would naturally fall at that point of the sentence. Even if the abbreviation has a period at the end of it, it’s still important to include the comma if it belongs there.

comma after abbreviation

To help you visualize this idea, you can refer to the following:

  • Jake, T.J., and Matt all wanted to go to the event.
  • I went to the C.D.C., but I found out nothing of note.

As you can see, when a period is used to break up an abbreviation or acronym, it must also be included at the end of the abbreviation. Since you have not ended the sentence yet, you should continue it as normal.

If you’re writing it in a list or at the end of an introductory clause, you will also want to place a comma directly after the period. This might look a bit dodgy to most readers because we’re conditioned to end a sentence after a period, but it’s grammatically correct nonetheless.

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When to Use A Comma after Abbreviations

There are three main reasons you would include a comma after an abbreviation. Most of the time, it’s because you’re using it in a list. There are some other options that can make it work, though.

In a List

If you include an abbreviation as part of a list, you typically want to place a comma after it. If it’s in the middle of a list, you’ll need to place that comma afterward to show that there is more to the list.

  • My friends Jack, T.K., and Bennet will all be coming along later today.
  • I went to A.Z., P.S., and B.A. for my lessons today

If you don’t include the comma, it will make a list look quite strange:

  • Incorrect: I went to A.Z. P.S. and B.A for my lessons today.

If you replaced the abbreviations with regular words, you’d see why the list looks so jarring:

  • Incorrect: I like apples oranges and pears.

As you can see, without commas, lists are difficult to read. That’s why they’re needed for abbreviations.

Introductory Clause

If your abbreviation comes at the end of an introductory clause, you should place a comma after it. It’s the same rules that apply whenever you’re using an introductory clause to introduce a phrase to the sentence before conveying your main point.

  • According to T.Y., there are a few reasons why you would want to continue with that.
  • Due to S.K.A., it’s been really hard for any of us to make amends with these issues.

Before a Parenthetical Element

You might also find that an abbreviation comes before a parenthetical element. When this happens, it’s appropriate to include commas on either side of the parentheses. That would mean that you have to place a comma after the abbreviation to start it.

  • My friend D.K., who I’ve known for years, will be coming today.
  • I work for F.E.D., which you should know, and I’ll be happy to help you out.

When to Not Use A Comma after Abbreviations

You should not use a comma after abbreviations when they fall naturally in a sentence, and commas wouldn’t be used there. You’ll want to make sure that commas are avoided if they break up the flow of your writing.

As a Title

When you use a title abbreviation, like “Mr.” or “Mrs.,” you generally do not want to follow them with commas. This would stop your sentence from having a good structure, making it very difficult to read.

  • Correct: I want to see Mr. Smith later today.
  • Incorrect: I thought Mrs., Juliet was going to be there.

Essential to the Sentence

Sometimes, abbreviations just fall in the middle of the sentence. You do not need to punctuate them when this happens, just like how you wouldn’t punctuate any other word if it is in the middle of the sentence.

  • Correct: I wanted you to look at her I.D. before you left.
  • Incorrect: I’m not giving you a D.U.I., without good reason.

As a Measurement or Suffix

If you’re using an abbreviation as a measurement, you’ll want to avoid using a comma unless it works. Common measurements like “cm.” and “kg.” have periods after them. They don’t often need commas after the period, though.

  • Correct: I measured it, and it was 14 cm. from the bottom.
  • Incorrect: I thought she weighed in at 55 kg., the last time we checked.

Comma after “Co.”?

You should place a comma after “co.” when it is used as part of an introductory clause or within a list. If it falls naturally in the middle of a sentence that wouldn’t usually call for a comma, then there is no reason to include the comma after the abbreviation.

  • With comma: According to Mark and Co., you needed to get this done by Friday last week.
  • Without comma: I’ll be speaking to Tim & Co. later today to find out more about this.

Comma after “Jr.”?

You do not need to place a comma after “Jr.” in most cases. It follows the title rules that work with “Mr.” and “Mrs.,” meaning that a comma does not belong after it (unless you include it as part of a list). It’s best to avoid the use of commas for this one.

  • Correct: I want to speak to Marty Jr. because I think he’ll be able to help me.
  • Incorrect: Darren Jr., said that you were going to be able to help us all out.

Final Thoughts

There is nothing grammatically incorrect about including a comma after a period with an abbreviation. As long as it fits the sentence (i.e. by being part of a list or introductory clause), then you can include a comma. If the comma doesn’t make sense, you should not use it.