How to Use a Period in Writing

The period, or 'full stop' in British/Commonwealth English, is one of the most basic punctuation marks you'll use. There are some rules for using it, although they're more straightforward than the rules for using a comma or semi-colon. The...

Ending Sentences with Periods

Mark the end of a sentence with a period. In English, most complete sentences consist of a subject, a verb, and an object. If the sentence isn't either a question or an exclamation, you place a period at the end. This mark signifies to a reader that one complete thought has ended and another will potentially begin.^{[2] X Research source}
1. For example, suppose you wrote: "My sister does yoga every morning." This is a complete thought with a subject ("my sister"), a verb ("does"), and an object ("yoga"), as well as an additional clause that tells the reader when the subject performs the action ("every morning"). Therefore, a period after the word "morning" is appropriate.
2. Note that "My sister does yoga" would also be a complete thought. However, the phrase "every morning" is part of the sentence since understanding it is dependent on the rest of the sentence.
Tip: You can also use periods after sentence fragments, or even single words, if you want to add emphasis or insert a dramatic pause in your writing. This technique is best used sparingly in formal writing.
Add periods to lists if each item is a complete thought. When making a bulleted list, you normally don't need periods at the end of each list item. However, if each list item is a full sentence, put a period at the end of each one (and start the first word with a capital letter).^{[3] X Research source}
1. The same rule applies if you start the list with a clause and each item in the list finishes that clause. For example, if you wrote "A period is necessary when:" each of the bullet points that ended that sentence would require a period at the end.
2. If, on the other hand, your bulleted list items are all sentence fragments or single items, you normally don't need a period anywhere.
Use periods for indirect questions. Normally, if you're writing a question, a question mark goes at the end. However, if the statement isn't a direct question, use a period instead.^{[4] X Research source}
1. For example, suppose you wrote, "I wonder if my friends are planning a surprise party." The direct question would be "Are my friends planning a surprise party?" By adding the phrase "I wonder" with the conditional "if," you create an indirect question.
2. The same goes for questions asked by other people. For example, you would place a period at the end of the sentence "Sarah asked if we were meeting on Monday." However, if you quoted Sarah, you would write "'Are we meeting on Monday?' Sarah asked."
Type a single space after a period. In the days of manual typewriters, it was common for people to put two spaces after every period. However, with computers, this is no longer necessary and can actually make writing more difficult to read.^{[5] X Research source}
1. Some fonts, such as Courier, allot the same amount of horizontal space for every letter. Occasionally, you'll still run across the guidance to place two spaces after a period if you're using one of these types of fonts (called "monospace fonts"). However, this is a rare exception.

Including Periods with Other Punctuation

Place a period within closing quotation marks. Generally, when you have a period next to quotation marks, the period goes inside, or before, the closing quotation marks — not after. In American English, this is true regardless of whether the quoted words are, themselves, a full sentence.^{[6] X Research source}
1. For example, you might write: The girls couldn't decide whether to watch "Legally Blonde" or "Never Been Kissed."
2. In British English, place the period within the closing quotation marks only if the quoted material would require it. Otherwise, the period goes outside the quotation marks.^{[7] X Research source} For example, you would write: Kelly's favorite movie is "Casablanca". Since Casablanca is not a sentence and doesn't require a period at the end, the period goes outside the quotation marks.
Change the period to a comma before a dialogue tag. When you're writing a conversation between two characters, you typically use dialogue tags to indicate which character is speaking. If the statement ends in an exclamation point or a question mark, you would use that punctuation inside the closing quotation marks, then add a period after the dialogue tag. However, if the statement made by the character would normally end with a period, you would use a comma inside the quotation marks instead.^{[8] X Research source}
1. For example, you might write:
  "When are we leaving for the beach?" Mary asked.
  "We'll leave in one hour," Katie replied.
2. The system for punctuating dialogue is the same in both British and American English.^{[9] X Research source}
Combine 3 periods together to form an ellipsis. An ellipsis is a different punctuation mark made by the combination of 3 periods. If you're quoting from another work, such as a research source, an ellipsis indicates that you left out words that appeared in the original. When writing dialogue, you might also use ellipses to indicate that the speaker trailed off or didn't complete their original thought.^{[10] X Research source}
1. For example, you might write:
  "When are we going to be able to go to the sushi restaurant again?" Katie asked.
  "I really don't... Hey, listen! Why don't we try to make sushi at home? It could be fun!" Mark replied.
Tip: Some style guides advise adding a fourth period to indicate that the sentence ended with ellipses.

Abbreviating with Periods

Use periods with most abbreviations in American English. Usually, when you abbreviate a word in American English, you'll add a period to the end. This is usually true regardless of whether the abbreviation uses initial letters or just a shortened version of the word. However, some commonly known abbreviations don't require periods.^{[11] X Research source}
1. For example, you would add periods to abbreviations such as "a.m." or "Mr."
2. Common names for institutions, corporations, organizations, and objects typically don't take periods. Examples include "CIA," "VCR," IBM," and "PTA." When in doubt, think about whether you recognize the entity immediately from the abbreviation or see it referred to by its full name just as often.^{[12] X Research source}
Tip: Some style guides favor omitting periods from abbreviations made up solely of uppercase letters, such as "MD" or "FBI," while others prefer that you leave them in. For most everyday writing, either usage is considered correct.
Omit periods from titles or abbreviations taken from first letters in British English. British English diverges from American English when it comes to using periods with abbreviations. Courtesy titles, such as "Mr" or "Ms," are not followed by a period in British English.^{[13] X Research source}
1. The title "Dr" also isn't followed by a period in British English.
2. Academic degrees and other designations that follow someone's name are listed in all-caps without periods, such as "MBA," "DPhil" (Doctor of Philosophy), or "BA" (Bachelor of Arts).
Add a space after the period for people's initials. When typing someone's initials instead of their full name, the initial letter is typically followed by both a period and a space. If you're typing a person's name with initials in a paper, make sure there's not a line (or page) break in between the initials.^{[14] X Research source}
1. If you find that a person's initials are broken across two lines (or worse, two pages), work with your page formatting to keep that from happening. Otherwise, your readers are likely to get confused.
Exception: If you're talking about a famous person who is commonly known by their initials, you can omit the periods. For example, you would write "JFK" or "MLK," but you would retain periods with "W. E. B. DuBois."
Leave out periods in acronyms. Acronyms are abbreviations, typically using the first letter of each word, that are pronounced as a different word. Since the abbreviation effectively becomes a word itself, periods are no longer appropriate between the letters.^{[15] X Research source}
1. For example, NATO is actually an abbreviation that stands for "North Atlantic Treaty Organization." However, it's pronounced NAY-TOH, not EN-AY-TEE-OH. For this reason, no periods are necessary between the letters.
2. Other examples of acronyms that don't need periods include NASA, AIDS, and laser (which stands for "light amplification by stimulated emission of radiation").