Are AM and PM Capitalized?


The abbreviations a.m. and p.m. are generally lowercased in running text, but they may also be capitalized (for example, in headings, signs, and notices). When lowercased, the letters of the abbreviations are usually followed by periods; if capitalized, periods are omitted.

  • 8:30 a.m. to 5:30 p.m.
  • 8:30 AM to 5:30 PM

Also, if you do capitalize these abbreviations in a document, consider using small caps to improve readability: 10 AM instead of 10 AM.

Abbreviations a.m. and p.m.

The abbreviations for time, a.m. (ante meridiem, or before noon) and p.m. (post meridiem, or after noon), refer to the two 12-hour periods of the day.

  • Maya woke up at 6:30 a.m. today.
  • Maya left work at 6:30 p.m.

Use a.m. and p.m. with numerals to emphasize exact time. These two abbreviations are commonly used in official and academic documents. In informal communication, we often use words instead.

  • Formal:The meeting is at 9:30 a.m. on Tuesday.
    Informal:It’s half past nine in the morning, and our heroes are fast asleep.


In running text, a.m. and p.m. are generally lowercased, with periods after each of the letters. But these abbreviations may also be capitalized—for example, in headings, signs, and notices.

  • The train leaves Zagreb at 9:20 p.m. and reaches Ljubljana at 11:39 p.m.
  • At 5:17 a.m. today, all the world’s clocks stopped.
  • Open weekdays: 9 AM to 9 PM
    sign on a storefront

Most style manuals (like the Chicago Manual of Style and AP Stylebook) suggest using lowercase instead of capital letters for a.m. and p.m. If you do use capital letters in running text, Chicago suggests using small capital letters (small caps) to improve readability.

  • The president will address the nation at 6:30 PM today.

Use of periods

Use periods in the lowercase abbreviations a.m. and p.m., but omit the periods when you capitalize these abbreviations.

  • Moonrise is at 5:23 a.m. tomorrow.
  • We usually take a break at 2:15 p.m.
  • It rained frogs from 11:25 AM to 1:03 PM.
  • She has a plane to catch at 3:25 PM tomorrow.

If the lowercase abbreviation a.m. or p.m. appears at the end of a sentence, don’t use two consecutive periods to end the sentence. Just the one period suffices both to mark the abbreviation and end the sentence.

  • Incorrect: We left at 4 a.m..
    Correct: We left at 4 a.m.

In British usage, periods are sometimes omitted even in lowercase abbreviations (At 4 pm, we serve thinly sliced cucumber sandwiches and scones with clotted cream).

Other Latin abbreviations

Many Latin abbreviations use lowercase instead of capital letters.

  • e.g. (exempli gratia, or for the sake of example)
  • i.e. (id est, or that is)
  • ibid. (ibidem, or in the same place)
  • etc. (et cetera, or and the rest)
  • et al. (et alii, or and others)

Whether an abbreviation is capitalized depends more on convention than on a fixed set of rules. For example, many abbreviations in the world of information technology are capitalized (IT, URL, PC), while the sciences often use a mix of capital and lowercase letters (mRNA, GlcNAc). Follow the conventions of your field, and stay consistent in usage throughout a document.

Quick Quiz

Which is preferred in American usage?
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Which is better style?
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