Acronyms speed up writing — until they slow down readers. The trick is knowing which ones to introduce, which to assume, and how to handle plurals, possessives, and punctuation. This guide covers the rules that hold across AP, Chicago, and MLA style.
Common Style Differences
| Item | AP Style | Chicago | MLA |
|---|---|---|---|
| U.S. / US | U.S. (with periods) | US (no periods) | US (no periods) |
| Plural acronyms | APIs (no apostrophe) | APIs (no apostrophe) | APIs (no apostrophe) |
| First-use spellout | Required unless universal | Required for unfamiliar | Required unless universal |
| "e.g." and "i.e." | Avoid in body | OK with commas | OK with commas |
| Doctor / Mr. | Dr., Mr. (periods) | Dr., Mr. (periods) | Dr. Mr (no period UK) |
The First-Use Rule
Spell out the full term, follow with the acronym in parentheses, then use the acronym for the rest of the document: "the World Health Organization (WHO) recommends…". Reset the rule for new sections in long documents — readers don't always start at the top.
Plurals and Possessives
- Plural: add lowercase 's' — URLs, CEOs, APIs.
- Possessive: add apostrophe-s — the CEO's announcement, the API's response.
- Plural possessive: apostrophe after the s — the CEOs' meeting.
- Never: CEO's as a plural — this is the most common error in business writing.
When to Skip Acronyms
- The term appears only once or twice — just write it out.
- The audience won't recognize the spelled-out version either.
- The acronym is offensive, controversial, or ambiguous in another field.
- You're writing for a general audience and the acronym is industry jargon.
Check Your Copy's Clarity
Acronym-heavy text often scores poorly on readability — check yours.
Readability Checker →