Chicago vs AP Style Capitalization – The Differences

If you write for a publisher, a university press or most magazines, your editor follows The Chicago Manual of Style. If you write for a newspaper, a wire service, a press office or a marketing team, your editor follows the AP Stylebook. Both guides capitalize titles. They do not capitalize them the same way, and the differences show up in almost every title longer than four words.

The core rule in each guide

Chicago (headline style): capitalize the first and last word and every major word. Lowercase articles, coordinating conjunctions, the infinitive to, as, and every preposition regardless of length.

AP (composition titles): capitalize the principal words, including prepositions and conjunctions of four or more letters. Lowercase articles and words of three letters or fewer, unless they are the first or last word.

Put the two side by side and the pattern is obvious. Chicago decides by part of speech. AP decides by length.

Difference 1: long prepositions

This is the big one. With, from, into, over, between, through, without:

• Chicago: A Conversation with My Father
• AP: A Conversation With My Father
• Chicago: Walking through Fire
• AP: Walking Through Fire

Readers used to AP often think the Chicago version looks under-capitalized. Readers used to Chicago think the AP version looks like a press release. Both are following their rule book.

Difference 2: short verbs and pronouns

AP's length rule has a well-known exception. Verbs, however short, are principal words and are capitalized: Is, Be, Do, Go. So are pronouns like It and He. Chicago reaches the same result by its part-of-speech rule. On this point the two guides agree, but it trips up people who have reduced AP to "capitalize anything with four letters": Who Is It For has three two-letter capitals and one lowercase preposition.

Difference 3: subordinating conjunctions

Chicago capitalizes If, Because, Although, That, When. AP capitalizes the long ones by the length rule and lowercases if:

• Chicago: What to Do If the Power Fails
• AP: What to Do if the Power Fails

Difference 4: hyphenated compounds

Chicago has a detailed rule. Capitalize the first element. Capitalize the following elements unless they are articles, prepositions or coordinating conjunctions. If the first element is a prefix that cannot stand alone (anti-, pre-, co-), lowercase the second element unless it is a proper noun. Spelled-out numbers capitalize both parts: Twenty-One.

AP is briefer and in practice most AP-style newsrooms capitalize both halves of a hyphenated compound when both are principal words: Long-Term, Self-Driving, Well-Being.

In everyday titles the two guides land in the same place: Self-Esteem, Follow-up, Pre-school. The capitalization tool handles the common compounds the same way in both styles, and flags nothing, so look twice at any compound starting with a prefix.

Difference 5: headlines are not titles in AP

This one causes more confusion than any rule. AP's capitalization rule is for composition titles: the names of books, films, songs, television programmes and so on when they appear in a story. It is not a headline rule. Most AP-style news organisations write their headlines in sentence case: Council approves new bridge after six-hour meeting. If you are writing a news headline and reaching for AP title case, check your publication's own headline style first. Many marketing teams use AP title case for blog post titles and sentence case for everything else, which is a reasonable compromise.

Chicago, by contrast, uses headline style for the titles of works and allows sentence style where a publisher asks for it. Chapter titles and headings inside a Chicago-style book are usually in headline style.

Where they agree

• The first word is always capitalized.
• The last word is always capitalized, however short.
• The first word after a colon is always capitalized.
• A, an, the, and, but, or, nor, for are lowercase in the middle.
• Proper nouns keep their capitals, and brand names keep their own casing (iPhone, eBay).

Which one should you use?

Use whichever one the reader will measure you against. A manuscript going to a publisher: Chicago. A press release, a news story or a corporate blog with a style guide based on AP: AP. A website with no stated style: AP title case for page titles is the common default, and sentence case for headings inside the page.

And when a title is already written and you need it in the other style, paste it into the converter, switch the tab from Chicago to AP or back, and copy. The prepositions are the part that changes, and that is the part the tool does for you.