Chicago Title Capitalization

What CMOS title case is

Chicago Manual of Style title case (CMOS, currently in its 18th edition as of 2024) is the most widely adopted title-case standard in U.S. publishing. The rules are simpler than AP title case and more permissive than MLA, which is why it's the default for book titles, academic journals, and most editorial outlets.

The core rules:

• Capitalize the first and last word of the title, regardless of part of speech.
• Capitalize all nouns, pronouns, verbs (including "is" and other forms of "to be"), adjectives, adverbs, and subordinating conjunctions.
• Lowercase articles (a, an, the), short prepositions (under five letters: at, by, in, of, on, to, up, via), and coordinating conjunctions (and, but, or, for, nor, so, yet) - unless they are the first or last word, or follow a colon.
• Capitalize "to" in infinitives (as a particle, not a preposition).

The CMOS 18 update (2024) tightened the short-preposition list to under five letters and added a few more explicit lowercase entries. This tool implements the 18th-edition rules.

CMOS vs AP vs APA vs MLA title case

The four major U.S. style guides each have a different title-case spec, and the differences come up often enough to be worth knowing:

• CMOS (Chicago). Capitalizes major words, lowercases articles, short prepositions (under five letters), and coordinating conjunctions. Permissive about prepositions.
• AP (Associated Press). Newsroom standard. Capitalizes all words four letters or longer (regardless of part of speech) plus all major words. "With" gets capitalized in AP but not in CMOS.
• APA (American Psychological Association). Used in social-science journals. Capitalizes all words four letters or longer, all major words, and any word after a colon. Lowercase articles and short prepositions.
• MLA (Modern Language Association). Used in humanities. Similar to CMOS but capitalizes all conjunctions and prepositions of four letters or more.

For most editorial work outside of journalism and academia, CMOS is the safe default. For news, use AP. For psychology journals, use APA. For literary scholarship, use MLA.

Edge cases the tool handles

Title case looks simple until you hit the edge cases. The tool handles:

• Words after a colon. Per CMOS 18, the first word of a subtitle (after a colon) gets capitalized even if it would otherwise be lowercase. The tool detects colons in the input and capitalizes the next word.
• First and last word. Always capitalized, even if it's "the" or "of".
• Hyphenated compounds. Both halves of a closed hyphenated compound get capitalized (e.g., "Self-Esteem", "X-Ray").
• Contractions and possessives. Apostrophes don't split words; "don't" capitalizes as "Don't", not "Don'T".
• Acronyms. The tool preserves all-caps tokens (it lowercases everything before re-titling, which loses acronym casing - a known limitation; type your input in lowercase for cleanest output).

When NOT to use title case

Not every heading deserves title case. Sentence case (capitalize only the first word and proper nouns) is becoming more common in product UI, marketing copy, and some editorial outlets because it scans faster and looks less shouty. Use sentence case for:

• Buttons, menu items, and other UI labels.
• Form field labels.
• Marketing landing-page headings (current consensus across SaaS).
• Email subject lines in casual marketing.

Use title case for:

• Book titles, journal articles, and other formal publications.
• Blog post titles (most CMSs default to title case).
• Section and chapter headings in long-form content.
• Movie, TV show, and song titles.
• Course titles, conference talk titles, and similar formal naming.

If your style guide explicitly mandates one or the other, follow that. If you're choosing fresh, pick whichever fits the tone of the surface.