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Guide

Title Capitalization: AP vs Chicago vs APA

·7 min read

Ask four editors to capitalise the same headline and you can get four different answers — all defensible. That is because AP, Chicago, APA, and MLA each draw the line in a slightly different place.

Here is what each actually specifies, and how to stop relitigating it every time someone writes a heading.

What all four agree on

The common ground is larger than the disagreement:

  • Capitalise the first word of the title, always.
  • Capitalise the last word of the title (AP, Chicago, MLA — APA is looser here).
  • Capitalise all nouns, pronouns, verbs, adjectives, and adverbs.
  • Lowercase the articles: a, an, the — unless first or last.
  • Lowercase the coordinating conjunctions: and, but, or, nor, for, yet, so.
  • Capitalise the first word after a colon in a subtitle.

So The Rise and Fall of the Third-Party Cookie is correct in every style. The arguments start with prepositions.

Where they differ

StylePreposition ruleExample
APCapitalise prepositions of 4 letters or moreA Guide Over the Bridge
ChicagoLowercase all prepositions, any lengthA Guide over the Bridge
APACapitalise words of 4 letters or moreA Guide Over the Bridge
MLALowercase all prepositions, any lengthA Guide over the Bridge

So the split is really two camps: AP and APA use a length rule, while Chicago and MLA lowercase prepositions regardless of length.

Which style should you use?

  • AP — journalism, news, press releases, most corporate communications.
  • Chicago — book publishing, long-form non-fiction, humanities.
  • APA — psychology, education, social sciences.
  • MLA — literature, languages, humanities coursework.

If nobody is imposing one on you, use AP. It is the most widely recognised, and its four-letter rule is easier to apply consistently than "is this word functioning as a preposition here?" — a question that produces genuine disagreement among professionals.

The cases that trip everyone up

Phrasal verbs. In "Look Up the Answer", up is part of the verb, not a preposition, so it is capitalised in every style. Compare "Walk up the Hill", where up really is a preposition. This distinction requires reading for meaning and no automated tool gets it reliably right.

The word "is". Short, but a verb — always capitalised. So is "Be", "Am", and "Are". People lowercase these constantly because they look like function words.

Hyphenated compounds. Chicago capitalises both parts of most compounds: Third-Party Cookie. AP does the same. But prefixes attached to a word stay lowercase after the hyphen: Re-entry, not Re-Entry.

"As". Lowercase in Chicago and MLA. In AP, it is only two letters, so also lowercase. Universally lowercase in practice.

Title case is not the only option

Worth noting that the whole debate is avoidable. Most software companies, and a growing number of publications, have moved to sentence case for headings — capitalise the first word and proper nouns, nothing else.

It reads faster, has zero edge cases to argue about, and translates cleanly into languages that have no title case at all. If you are writing product copy, documentation, or UI labels, sentence case is the safer default. Title case still belongs on article headlines, book titles, and academic paper titles.

For more on that trade-off, see our guide on title case vs sentence case.

Applying it without thinking about it

Our title case converter implements the common ground between AP and Chicago: first and last words capitalised, short articles, conjunctions, and prepositions lowercase in the middle, everything else capitalised. That matches both guides for the large majority of real headlines.

Two things it deliberately does not do: it cannot tell a phrasal verb from a preposition, and it will not know that your product name has an unusual capitalisation. Convert first, then scan the result — it is seconds of checking against minutes of manual work.

If you want every word capitalised without editorial exceptions, use Capitalized Case instead. That is right for short labels and data columns, and wrong for headlines.

The rule that matters most

Pick one style, write it down, and apply it everywhere. Mixed capitalisation across a single site is far more noticeable — and looks far more careless — than any individual style choice. Nobody has ever bounced from a page because it used Chicago rather than AP. Plenty have noticed when three headings on one page were capitalised three different ways.

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