Are A.M. and P.M. Capitalized? What Do They Mean?

There’s a lot of confusion surrounding “A.M.” and “P.M.” Are A.M. and P.M. capitalized? Do you write them with periods or without? You’ve come to the right place.

What Is the Full Form of A.M. and P.M.?

A.M. means “ante meridiem” and P.M. means for “post meridiem”, which are Latin phrases meaning before midday, and after midday. Therefore, you use the abbreviation A.M. after a time to refer to any time before noon but after midnight (i.e., the morning). The abbreviation P.M. is used to refer to any time after noon until midnight (i.e., the afternoon, evening, and night).

An alternative to using A.M. and P.M. in times is to use the military time where the clock is divided into 24 hours instead of periods of 12.

Are A.M. and P.M. Capitalized in Sentences?

According to all of the major style guides, a.m. and p.m. should be lowercased and the letters should be separated by periods when used in sentences.

Style guides also recommend separating the time numeral from the abbreviation with a space. Also, timezones spelled out should be separated by a comma after the abbreviation.

Like these other acronyms, that also means you should leave out any punctuation or periods. Here are some examples of sentences with A.M. and P.M.

  • I woke up at 5 a.m. to go for a run.
  • Let’s agree to meet for lunch at 3 p.m.
  • Did you say the movie starts at 10? Is that a.m. or p.m.?
  • We’ll go to the club at 10 p.m., central time?

Here are some common mistakes and incorrect examples.

  • Is the game at 9 pm? – Abbreviation is not separated by periods.
  • He wakes up every day at 10 A.M. – Abbreviation is capitalized.
  • She called me last night at 6p.m. – No space after time numeral.

Notice that some of these examples are commonly used, and may not stand out as being wrong. People often lowercase a.m. and p.m. in casual or informal writing, so it doesn’t really matter how you stylize them.

Note: Despite the official guidance from style guides, you can still use AM and PM if you wish. For example, you could write “1:00 PM” if you choose. Just know that it’s not advised by the official style guides.

The table below summarizes capitalization and style rules for some of the leading style guides.

Style GuideCapitalized?Period Between Letters?Space After Numeral?
MLALowercaseYesYes
APALowercaseYesYes
APALowercaseYesYes
ChicagoLowercase or small capsYesYes
AMASmall capsNoYes
MHRALowercaseNoNo

Are A.M. and P.M. Capitalized in Titles?

Titles and headlines are different. The abbreviations A.M. and P.M. should be capitalized in titles. However, the abbreviations should still have periods between the letters and the time numerals should be separated from the abbreviation by a period. In titles, words over four letters, in addition to words that are important, are capitalized. Although A.M. and P.M. are two letters in length, they should be capitalized in a title.

Here are some examples:

  • 5 A.M. at the Airport: A Novel
  • We Met at 3 P.M. That Day
  • I’ll See You in the A.M.

Conclusion

There you have it. The answer to “are a.m. and p.m. capitalized” depends on whether the abbreviation is being used in a sentence (lowercased) or a title (capitalized).


Capitalize My Title is a dynamic title capitalization tool used to make sure your titles or headlines use proper capitalization rules according to various style guides include APA, AP, MLA, and Chicago. It also counts your words and checks for grammar issues.

1 COMMENT

  1. Hello,

    I’m curious as to how you came to the conclusion that a.m. and p.m. should be capitalized without periods when APA, Associated Press, MLA, and Chicago Manual of Style all say that lowercase with periods (the way I wrote it) is correct? Barring, of course, the caveat by Chicago Manual of Style that it is okay to capitalize the two only when it is with periods and only when it is small capitals.
    Thanks.

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