GUIDE · CASE

Title Case across style guides: AP, Chicago, APA and Wikipedia

By ShengFeng · Published 2026-10-15 · Last updated: 2026-10-15

Every style guide agrees that a title should capitalize its principal words and leave the small ones alone. They disagree about which words are small. The result is that the same headline is correct in one house style and wrong in another, and an automatic converter can only ever produce one of the possible answers. This guide sets out where the guides agree, where they diverge, and how to get from an automatic result to a compliant one.

Where the guides agree

The common ground is larger than the disagreements, and it is worth stating first because it covers most of a typical title.

• Capitalize the first word and the last word, whatever part of speech they are.
• Capitalize nouns, pronouns, verbs, adjectives and adverbs — the words that carry the meaning.
• Lowercase articles: a, an, the.
• Lowercase coordinating conjunctions: and, but, or, nor, for, yet, so.
• Lowercase short prepositions: of, in, on, at, to, by, for, with, from.
• Capitalize the first word after a colon in most guides, though not all.

Where they diverge

Hyphenated compounds in practice

Hyphenated words are where the divergence bites hardest, because a title often contains several of them and the guides pull in different directions. Under Chicago, the first element is always capitalized and later elements are capitalized only if they are principal words, so “State-of-the-Art” and “Cost-Effective” both come out as written. Under APA, both parts are capitalized, which gives the same result for those two examples but differs on compounds whose later element is a small word. The practical consequence is that you cannot verify a hyphenated title by eye against a single mental rule; you have to know which guide you are following.

What the converter does, and how to reconcile it

The Title Case action capitalizes the first letter of every word, where a word starts at the beginning of the text or after any character that is not a letter or a digit. That is the “capitalize everything” position — no guide's finished answer, but a useful starting point that is closer to the target than raw mixed input.

Reconciling it with your guide is then a small, mechanical job:

1. Convert first so every word starts capitalized and the title is visually uniform.
2. Lowercase the articles, conjunctions and prepositions your guide treats as small words. There are usually only two or three in a headline.
3. Apply the hyphen rule of your guide to any hyphenated compound.
4. Check the first and last words are capitalized regardless of what they are.
5. Check the word after a colon, since that is where the guides most often diverge in practice.
6. Restore proper nouns and acronyms that the conversion lowercased, such as a product name or an initialism.

A short worked example

The same title under three guides, using the converter as the first pass:

after Title Case:
  A Guide to the State-of-the-Art Tools for Data Entry

AP (capitalize prepositions of four or more letters):
  A Guide to the State-of-the-Art Tools for Data Entry

Chicago (lowercase all prepositions):
  A Guide to the State-of-the-Art Tools for Data Entry

Wikipedia (lowercase prepositions of fewer than five letters):
  A Guide to the State-of-the-Art Tools for Data Entry

In this example the three guides coincide, which is common for short titles with no awkward prepositions — and is exactly why people underestimate the differences. A title containing “through”, “between” or “according to” will separate the guides immediately. The full rule set behind the conversion, including what happens to hyphens and acronyms, is described in the case conversion guide.

When sentence case is the safer default

Title Case is not always the right answer, and the guides themselves acknowledge it. Most modern style guides now use sentence case for many kinds of heading — particularly headings that sit inside running text, subheadings, and anything that reads as a sentence rather than a label. Title Case remains standard for book and article titles, for the names of publications, and for display headings that are scanned rather than read. So the first question is not which title-case rule to follow, but whether the heading should be in title case at all.

The simplicity of sentence case is worth taking seriously. It has essentially no ambiguity — there are no questions about prepositions, hyphens, or the word after a colon — which makes it the one style an automatic converter can produce almost correctly. If a heading must be in Title Case, expect to make a handful of manual decisions per heading. If it can be in sentence case, the conversion is nearly final as it stands.

A quick reference you can keep

• First and last word: always capitalized, in every guide.
• Nouns, pronouns, verbs, adjectives, adverbs: always capitalized.
• Articles and coordinating conjunctions: always lowercase — a, an, the, and, but, or, nor, for, yet, so.
• Prepositions: lowercase in Chicago; capitalized at four or more letters in AP and APA; at five or more letters in Wikipedia.
• The word “to” in an infinitive: lowercase in Chicago and Wikipedia; capitalized in AP and APA.
• After a colon: capitalized in most guides; only when it begins a complete sentence in Wikipedia.
• Hyphenated compounds: both parts capitalized in AP and APA; first part always, later parts only if they are principal words, in Chicago.

Applying this without memorizing it

• Pick one guide per project and note it at the top of the document. Consistency matters more than which guide you chose.
• Keep a short list of the small words your guide lowercases, and search the document for them rather than reading every heading.
• Treat the converter as a first pass, never as a final answer, because no single rule set satisfies every guide.
• Check proper nouns last, after the mechanical fixes, since those are the errors a reader will actually notice.
• Do not mix guides within one document. A page where two headings follow different rules reads as carelessness even when each heading is individually defensible.