I came across the sentence "He visited Chicago many times when he lived in the U.S.", and seemingly the last period is for the ending of the sentence. So is "U.S" a correct abbreviation? This is a sentence from an exam question and I am a bit too curious.

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    @mcalex The two top answers don't disagree
    – LoremIpsum
    Dec 21, 2021 at 18:09
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    @LoremIpsum compare and contrast: in 'an exclamation or question, then the mark must be added after the period' with 'Questions and exclamations use question marks and exclamation points instead of a period, not in addition to one'
    – mcalex
    Dec 21, 2021 at 19:58
  • @smci: no, "U.S" is not correct. You need either two periods or none. (But at the end of a sentence, the second period does double duty as the sentence-ending period.) Also, "U.S." is not an acronym. If it were, it would be pronounced the same as the personal pronoun "us".
    – TonyK
    Dec 22, 2021 at 13:17
  • @TonyK: typo, obviously I meant "U.S." not "U.S". You're correct it's not an acronym.
    – smci
    Dec 23, 2021 at 5:38
  • To be clear, "U.S." is one correct abbreviation for "United States", and "US" is another, in part depending on whether you use BrE/AmE, also context (e.g. USPS vs U.S. Army). For reference, "US Army" is now 25x more common than "U.S. Army", increasing from 5x in 2004. Your question is not asking What are all the valid abbreviations for "United States"? only asking if it's correct to not put a second period at the end of a sentence which ends in an abbreviation which itself ends in a period.
    – smci
    Dec 23, 2021 at 5:39

4 Answers 4


The abbreviation is correctly shown as U.S. A sentence must, as you understand, be ended by a period (full stop), question mark, or exclamation mark. If a sentence is ended by a period which is part of an abbreviation, then that single final period does double duty - it (1) indicates the abbreviation and (2) ends the sentence.

If the sentence is an exclamation or question, then the mark must be added after the period ending the abbreviation:

I want to live in the U.S.!
How long have you lived in the U.S.?

If a sentence ends with an abbreviation followed by a period, should I insert another period to mark the end of the sentence? (MLA Style Center)

Particularly outside the US, there is a modern tendency to write abbreviations such as US, BBC, UK, etc, without periods, and then the normal rules for ending a sentence are followed:

I often listen to the BBC.
I love the scenery in the UK!
Have you visited the US?

Punctuation in abbreviations (Lexico)

  • "U.S. Army" is a fairly common stamp/sign on military equipment, especially vintage.
    – Criggie
    Dec 20, 2021 at 5:48
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    In particular, the BBC refers to itself as "the BBC", without periods. Dec 20, 2021 at 13:47
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    @EspeciallyLime - As early as 1950 it was 'BBC' in its own publications, but I have see a pre-war TV test transmission showing 'B.B.C.'. Dec 20, 2021 at 14:31
  • @MichaelWokeHarvey When an abbreviation becomes common enough to be treated as a word of its own, it becomes an acronym or initialism (depending on whether it's pronounced as a word (e.g. SCUBA) or by saying the letters (as in TV or BBC)). These are written without periods.
    – Barmar
    Dec 20, 2021 at 15:09
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    I don't think the tendency to exclude the periods in acronyms is particular to outside the US. I live in the US and see it all the time (look, I do it myself). It is usually sufficient just to make sure each letter is capitalized.
    – Seth R
    Dec 20, 2021 at 16:50

You never end a sentence with a double period. This is written in many of the major style guides. For example, Chicago:

Why, after a lifetime (I trust) of never encountering two periods in a row, do readers suddenly think this might be a good idea? In any case, here are some answers: Don’t ever put two periods in a row. Put one period at the end of a declarative sentence, even if it ends with an abbreviation or a URL. (Questions and exclamations use question marks and exclamation points instead of a period, not in addition to one, even in quotations.)


A sentence should never have two periods at the end. If a sentence ends with an abbreviation followed by a period, do not add an additional period

Whether or not you should use "U.S." or "US" is a matter of style; both are used. In APA, you would use US unless it is being used as an adjective (and — again — you would not use a double period if it was at the end of a sentence).

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    Unless you're ending with an ellipsis.
    – Hearth
    Dec 20, 2021 at 0:13
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    @Hearth Strictly speaking, an elipsis is a different type of punctuation that is distinct from a period. It’s traditionally typeset with periods in English and other Latin scripts, though there is a distinct Unicode code point for it (U+2026, rendered as ‘…’ in whatever font you are viewing the page with). Dec 20, 2021 at 2:50
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    @Hearth Don't end a sentence with exactly two periods. Dec 20, 2021 at 7:34
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    @Acccumulation - don't end a sentence with any number of periods greater than one. Dec 20, 2021 at 13:03
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    You never end a sentence with a double period, period. Dec 20, 2021 at 19:22

Writing "U.S." always with periods has been prescribed by some style guides, including the Associated Press Stylebook, since forever. Other style guides allow "US" without periods, in which case there is no question of a double period when the abbreviation ends a sentence.

  • But in real-world usage, "US Army" is nowadays 25x more common than "U.S. Army", increasing from 5x in 2004. So, the style guides are outmoded on this point. And the longer the acronym, the sillier it would get: U.A.E., N.A.S.A., C.E.N.T.C.O.M. ...
    – smci
    Dec 21, 2021 at 23:29
  • I disagree that the style guides are outdated; they are not guides to what's in common usage. They are guides for particular publications to follow so as to have standard usage, which means they prescribe whatever they want, not what a google search turns up. Those other acronyms you list are not covered by the same rule in the AP Style Guide. NASA is NASA, FBI is FBI, but U.S. is U.S. to avoid confusion with the word "us".
    – user8356
    Jan 3, 2022 at 20:50
  • learners mistake the style guides for advice about on general everyday speaking/writing, which they aren't. Most of us aren't writing journalistic pieces, simply trying to communicate. Also, US style guides often differ with BrE, AusE, IndE etc. (Btw, in "U.S. Army" which is what I cited (rather than plain "U.S." on its own), it's incorrect that U.S. is U.S. to avoid confusion with the word "us")
    – smci
    Jan 3, 2022 at 20:58

These prior answers are good but I feel that they may be room for the OP (or subsequent searchers) to still feel that their question isn't being answered: "U.S." (two periods) is the norm in North America; "US" with no periods may be preferred by some style guides (one hopes not in all-caps contexts). In no event is "U.S" with only one period used...except that at the end of a sentence, we don't put double periods. This is not so much a grammar or spelling rule as it is a typographer's convention, much like the (now largely obsolete) placement of a period inside a quotation at the end of a sentence.

So in the quoted sentence, the author was essentially using "U.S." with two periods, and then needed to end the sentence with a period, and those periods got munged into one another. Basically the rule would be "when a sentence ends with an abbreviation that terminates in a period, drop the abbreviation's period before adding the sentence's period." As others have said, if the sentence uses something other than a period, the abbreviation keeps its period.

  • "[E]xcept at the end of a sentence"? I would say even at the end of a sentence. It's still "U.S." there, but as you say, the period after the S (which is there!) and the sentence-ending period are "munged" together. Other people say this is one period doing double duty. Two different ways of saying the same thing as far as I can see.
    – David K
    Dec 22, 2021 at 14:16

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