PhD, BA, AB, MA, MLitt, MD
NATO, AIDS, CEO
a.k.a. (for “also known as”)
AM, PM; or a.m., p.m. (use small caps for a more formal and easier-to-read look)
Periods with Abbreviations
- Use periods with abbreviations ending in lowercase letters: Dr., Ms., etc.
- Use periods with initials standing for a person’s name: J. R. Tolkien. Do not use periods with initials that replace the full name: JFK.
- No periods are used with abbreviations comprised of full capitals, even if lowercase letters appear within the abbreviation: PhD, MD, CEO
- In running text, use periods with traditional state abbreviations and the United States (U.S.) (see States)
General Use Guidelines
Use full words the first time the abbreviation or acronym is used in text, and place the abbreviation or acronym in parentheses immediately following.
Do not begin a sentence with an abbreviation. Exceptions: Mr., Ms., Mrs., Dr., and St.
Capitals vs. Lowercase
Initialisms used as nouns tend to be capped: HIV, UFO, FAQ
Over time, some longer initialisms become lowercased (radar). Refer to Webster’s when in doubt.
Abbreviations without periods take s, no apostrophe. Apostrophes may be used if misreading is a possibility.
Abbreviations with one period usually add the s before the period:
ed., eds.; yr., yrs.; Dr., Drs.
Abbreviations with more than one period use apostrophe s:
p.p.’s; the d.t.’s