The period goes inside parentheses (or brackets) if the entire sentence is contained within the parentheses. The period goes outside if the text within parentheses is part of a larger sentence.
Periods with parentheses
Place a period within parentheses (or round brackets) if the sentence ends inside parentheses—that is, if the parentheses contain an entire sentence.
- I decided to send them an email. (It was too late to call.)
The entire sentence is contained within parentheses and ends inside, which is indicated by a period.
- Make sure to check your airline’s baggage limit. (It should be written on your ticket.)
- We plan to study monotremes in Australia. (Monotremes are egg-laying mammals found in Australia and New Guinea.)
Place the period outside parentheses if theappears within a larger sentence. The period then ends the sentence to which the parenthetical phrase belongs.
- Half the world’s oxygen is produced by plant-based marine organisms (like seaweed and plankton).
The parenthetical text belongs to the larger sentence. The period is placed after the parentheses to end the sentence.
- I decided to send them an email (it was too late to call).
- Anita has moved to Australia to study monotremes (egg-laying mammals like the platypus).
Don’t place a period inside parentheses unless the entire sentence is contained within the parentheses.
- Incorrect: In this study, we investigate the nesting habits of monotremes (egg-laying mammals.)
Correct: In this study, we investigate the nesting habits of monotremes (egg-laying mammals).
Don’t leave the sentence outside parentheses unpunctuated.
- Incorrect: Please call me tomorrow (I’m free in the morning.)
Correct: Please call me tomorrow. (I’m free in the morning.)
Correct: Please call me tomorrow (in the morning if possible).
An entiremay be contained within parentheses. (An independent clause is one that can stand by itself as a sentence.) Whether you make it a sentence on its own or integrate it with a larger sentence depends upon how closely you want the two thoughts to be related.
- My cat Tooks loves cheese. (She also likes pizza.)
The parenthetical clause is a sentence on its own with its own period.My cat Tooks loves cheese (she also likes pizza).The parenthetical clause has been integrated with the larger sentence to indicate that the twoare closely related. Note the use of just a single period outside parentheses to end the larger sentence.
Periods with brackets within parentheses
Square brackets are used in American writing to show brackets within brackets. Sentences usually don’t end inside square brackets, but they may end in the parentheses to which the square brackets belong. You must then place the period outside the square brackets but within parentheses.
- Cats can read your mind. (See The Complete Guide to Cats .)
- Temperatures soared in July 2021. (It was the hottest July in 150 years [Table 1].)
The sentence could also end outside the brackets and parentheses (if the parenthetical text is part of a larger sentence), in which case the period goes outside. Remember not to leave a sentence unpunctuated.
- Cats can read your mind (see The Complete Guide to Cats ).
- Temperatures soared in July 2021 (the hottest July in 150 years [Table 1]).
In British writing, round brackets are used within round brackets. Place the period inside if the sentence ends within brackets, but outside otherwise.
- Cats can read your mind. (See The Complete Guide to Cats (1991).)
- Temperatures soared in July 2021. (It was the hottest July in 150 years (Table 1).)
- Cats can read your mind (see The Complete Guide to Cats (1991)).
- Temperatures soared in July 2021 (the hottest July in 150 years (Table 1)).
Parentheses (round brackets) are known as brackets in British English. In American English, square brackets are referred to as brackets.
Periods with abbreviations in parentheses
If an abbreviation that ends in a period appears within parentheses that are part of a larger sentence, place another period after the closing parenthesis to end the sentence.
- Please call me tomorrow (preferable before 6 p.m.).
- We publish all genres of fiction (fantasy, romance, historical, etc.).
However, if the sentence ends inside parentheses, don’t add another period. Just the one period suffices to end both the abbreviation and the sentence.
- Please call me tomorrow. (I’m free until 6 p.m.)
Other punctuation with parentheses
Other punctuation marks, like, , and also go inside if they belong to the text within parentheses or brackets, and outside otherwise. Check whether you are punctuating the text inside parentheses or the surrounding sentence.
- Let’s meet tomorrow (9 a.m.?).
- Parentheses are used similarly in British and American English (just that in British English, they are known as “brackets”).
- Remember all those boots we wore? (The nineties was a crazy time!)
- Can we meet tomorrow (about 9 a.m.)?
- “We make PFDs (portable floating devices).”
Commas, semicolons, and dashes always go outside if they appear at the end of parenthetical matter because they always belong to the surrounding sentence.
- Monotremes (egg-laying mammals), which are indigenous to Australia and New Guinea, are endothermic like other mammals.
- Don’t place a period both within and outside parentheses (round brackets); the sentence has already ended within parentheses.
- Be careful using punctuation with parentheses (round brackets)—writers often get it wrong.