Periods (.) end a declarative sentence: Periods end a declarative sentence.
Use to end a mildly imperative sentence: Use periods to end a declarative sentence.
Use inside quotation marks: “That’s a nice hat.” Quotes that are part of a complete sentence take a comma: “Your hat is hideous,” he said.
Use with acronyms that would otherwise spell a word: U.K., U.N., U.S.
Exceptions: EU, AP (a trademark for Associated Press)
Initials of names do not take periods: FBI, FOIA, JFK, MI5, ISIS
Initials in a name do take periods: John F. Kennedy, W.E.B. Du Bois. Note: Du Bois wrote his name with spaces between the letters (W. E. B.); it is written without spaces to avoid appearing on two different lines.
Use after abbreviated titles: Dr., Ms., Sr., Jr., Lt. Gov.
Use with time: 9 a.m., 7:52 p.m.
Use when abbreviating months: Jan. 5, Oct. 13
Part of a series on punctuation.