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

Only one of these forms is frequent enough to carry a rank in our corpus: "okay", at #930. "OK" appears in the dictionary data but not in the frequency sample, which is itself a signal about how rarely it turns up in running text. Source: PlainSpell corpus, Wiktionary (kaikki.org) headwords with FrequencyWords 2018 English ranks

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.

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.