OK: Style Guide Spelling Decisions (AP, Chicago, MLA, APA)

How major style guides rule on "OK"

AP firmly prefers 'OK' (no periods); Chicago and MLA accept both; the spelled-out form is more common in fiction.

The disagreement on "OK" is an example of register: formal style versus informal usage, the category of style-guide differences that most often confuses copy editors and creates inconsistency across long documents. Below is a guide-by-guide breakdown, drawn directly from the published editions cited.

What the divergence actually means

Unlike many compound-modernization decisions where style guides eventually converge, "OK" continues to show genuine divergence between major guides. The AP Stylebook treats this as a settled call; Chicago Manual leaves more flexibility; and Merriam-Webster, as a descriptive dictionary, records both forms. Source: Chicago Manual of Style, 17th Edition

The APA Publication Manual aligns with AP and Chicago on "OK", though APA generally addresses spelling questions only when they intersect with statistical reporting or technical psychology vocabulary. Where the manual is silent, APA defers to Merriam-Webster as its standard reference. Source: APA Publication Manual, 7th Edition

Merriam-Webster lists "OK or okay", which serves as the lexicographic baseline for U.S. style decisions. Because Merriam-Webster's entries reflect aggregated published usage rather than editorial preference, when a guide says "follow Merriam-Webster", as APA does, that effectively delegates the call to whichever spelling has dominated the published corpus. Source: Merriam-Webster Dictionary

Garner's Modern English Usage classifies the "OK" / "okay" pair on its Language-Change Index, a five-stage scale measuring whether a once-disputed form has been accepted into Standard English. For register: formal style versus informal usage, Garner's typically rates the dominant form at Stage 4 ("ubiquitous but objected to by traditionalists") or Stage 5 ("fully accepted"). Source: Garner's Modern English Usage, 5th Edition

Practical guidance for editors

For working writers, the practical rule is straightforward: in journalism, follow AP; in academic writing in the humanities, follow MLA or Chicago; in social-science publishing, follow APA; in book publishing, follow Chicago. When no house style applies, Merriam-Webster's main entry is the safest default. The differences across these guides on "OK" reflect not disagreement about correctness but different audiences and editorial pressures.

Editorial context

Journalistic traditions cemented "OK" as the compact form for headlines and body text by the mid-20th century, yet a pronounced register split endures in book publishing, where "okay" prevails in fiction and dialogue-heavy narratives for its smoother readability and phonetic alignment. Corpus analyses, including the Corpus of Contemporary American English, show "okay" comprising over 70% of instances in fiction subcorpora since 1990, versus "OK" dominating news text. This divergence persists because novelists prioritize voice and rhythm, "Don't worry, it'll all be okay," she whispered., over abbreviation economy, even as copy editors align manuscripts with house styles like Chicago's flexible allowance. The split highlights how formality yields to genre demands, with "okay" evoking casual intimacy that "OK" can disrupt in immersive prose.

Cross-references

For the dictionary entry, frequency data, and pronunciation of OK, see the main word page. For other style-guide spelling decisions in this category, browse all style-guide spelling rulings.