Punctuating Abbreviations: The Basics

Confused about abbreviations? Do you use periods between letters? When should you write out a phrase or term and when should you abbreviate it?

Before you do anything, check if your organization, school, or professor prefers one particular stylebook over another: Associated PressChicago Manual of StyleAMA, etc. If so, follow the guidelines in that stylebook.

However, a lot of us don’t follow a mandated stylebook. In that case, we hope this information is helpful to you. Also, remember that this is coming from someone who speaks American English. These rules may be different in other countries that speak English.

First, while we tend to refer to all these as “abbreviations,” there are three separate types: abbreviations, acronyms, and initialisms. Acronyms and initialisms are typically not punctuated.

AbbreviationsShortened version of a word or phrase where you say the whole word even though it’s not written in fullvs. (versus)
dept. (department)
corp. (corporation)
AcronymsFirst letter of each word is used in a phrase that is pronounced as a wordRADAR (Radio Detection and Ranging)
SCUBA (Self-Contained Underwater Breathing Apparatus)
PIN (Personal Identification Number)
InitialismsFirst letter of each word is used in a phrase that is pronounced letter by letter

FBI (Federal Bureau of Investigations)

AARP (American Association of Retired Persons)

EMT (Emergency Medical Technician)

General Rules for Punctuating Abbreviations

Names and titles
  • If using a middle initial in a name, use a period. If two successive letters are abbreviated, do not add spaces between the periods.
    • Examples: Dwight D. Eisenhower, Michael P. Jordan, J.K. Rowling, George R.R. Martin
  • If a full name is abbreviated, use only the first letters without periods.
    • JFK (John F. Kennedy), RBG (Ruth Bader-Ginsberg), FDR (Franklin D. Roosevelt)
Abbreviations for days and months

In formal writing, it’s best to not abbreviate these, but abbreviations are more acceptable in informal writing. In each case below, abbreviations should be punctuated by a period.

  • Days
    • Mon., Tues., Wed., Thurs., Fri., Sat., Sun.
  • Months
    • Jan., Feb., Aug., Sept., Oct., Nov., Dec. (March, April, May, June, and July are not abbreviated.)
    • June 27; Tues., Sept. 6

Stylebooks differ on time abbreviations.

  • Use a.m. or A.M., and p.m. or P.M. There are no spaces. If you do not follow a specific stylebook, choose one method and stick to it. It’s also best to write out the time, as in 7:00 P.M. (or p.m.), not 7 p.m.
    • Examples: 10:15 a.m.; 8:00 P.M.
  • Time zones: Do not punctuate time zones (EST, PST).
  • Time eras: This is a matter of preference. Some stylebooks recommend using periods between letters, others do not. Whichever you choose, stay consistent.
    • Examples: B.C., A.D., BCE
Academic degrees
  • Typically, use periods after the first initials in a degree
    • Examples: Associate of Arts: A.A., Associate of Science: A.S., Bachelor of Science: B.S., Master of Arts: M.A., Doctor of Medicine: MD
    • This gets a bit more complicated depending on specific degrees. You can find a helpful listing of every degree you can imagine at abbreviations.com.
  • Some exceptions:
    • If you use a phrase three times or fewer, it should be written out each time.
    • Commonly used abbreviations do not need to be written out. Check the Merrian-Webster dictionary: if an abbreviation appears as a noun, you do not need to write it out: IQ, HIV, REM
    • Generally speaking, do not use abbreviations in reference lists. Write out the phrase or name. For example, a source from the CDC should be written out as Centers for Disease Control and Prevention in a reference list. This also applies to headings, table titles, and figure captions.
    • When using an abbreviation for a unit of measure with numbers, simply use the abbreviation. There is no need to write out the term. (12 g instead of 12 grams). If you are only referring to the measurement without specific numbers, write out the term. (a few pounds).

Additional information

These are some general rules for punctuating abbreviations. If you are a writer and your organization does not follow a stylebook or have its own, we highly recommend buying or subscribing to one and using it. It is easier to make punctuation and other decisions easier when you have a guide that helps you maintain consistency in your writing.

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