The Editor’s Manual
Free learning resource on English grammar, punctuation, usage, and style.
Periods always go inside quotation marks in American usage. In British usage, a period (or full stop) goes inside only if the quotation is a complete sentence.
Use just one period, not two, after an abbreviation like “etc.” even when it appears in quotes at the end of a sentence. Don’t add another period after the closing quotation mark.
When an abbreviation like “etc.” appears in parentheses, place another period after the closing parenthesis to end the larger sentence. But if the entire sentence is enclosed in parentheses, use just one period, not two.
The abbreviations “UK” and “UN” are generally written without periods except in certain styles. The abbreviation “EU” is always written without internal periods.
The abbreviation for United States may be written with or without internal periods: U.S. or US. Both styles are acceptable.
Place a period within parentheses if the entire sentence is contained in the parentheses. Place the period outside if the parenthetical phrase appears within a larger sentence.
When an abbreviation ending in a period is followed by a punctuation mark like a comma, colon, semicolon, or dash, use both the period and the punctuation mark. But use only a single period after an abbreviation at the end of a sentence.
If an abbreviation ending in a period also ends a sentence, use just one period, not two. With parentheses, place a period after the closing parenthesis to end the larger sentence.
Periods are used when the abbreviations for time are lowercased (a.m., p.m.) but omitted when they are capitalized (AM, PM).
An ellipsis is a series of three dots. In a quotation, an ellipsis signifies omitted words. In a dialogue or narrative, the ellipsis shows faltering speech or a pause.