Content4 min read
AP vs Chicago Title Case: The One Rule They Actually Disagree On
The two style guides agree about almost every word in almost every title. The exception is prepositions of four letters or more, and that single rule is the whole difference.
AP vs Chicago title case is a smaller argument than it looks. Both capitalise the first and last word, both lowercase articles and the coordinating conjunctions, and on most titles they produce exactly the same string. The difference is prepositions of four letters or more — AP capitalises them, Chicago does not.
The one rule, in one table
| Word | AP | Chicago | Why |
|---|---|---|---|
the, a, an | the | the | Articles are down in both |
and, but, or | and | and | Coordinating conjunctions are down in both |
of, in, to | of | of | Short prepositions are down in both |
through | Through | through | The disagreement: four-plus letters |
between | Between | between | Same rule |
without | Without | without | Same rule |
is, are | Is | Is | Verbs are up in both, at any length |
AP's rule is a length rule: capitalise every word of four letters or more, plus all principal words, whatever part of speech they are. Chicago's is a grammar rule: lowercase articles, coordinating conjunctions and prepositions regardless of length, capitalise everything else.
So on a title with no long prepositions in it — which is most titles — the two are identical. On "Growing a Starter Through a Cold Winter" they differ by exactly one letter.
FreeMentioned in this article
Title Case ConverterAP, Chicago, APA and sentence case — and the words they disagree on.It applies AP, Chicago, APA and sentence case at once, and then lists only the words the three title styles treat differently, which is usually two or three.
Where APA sits
APA follows AP's four-letter rule, so for most purposes it produces the same title as AP. It has two additions worth knowing:
- Both halves of a hyphenated compound are capitalised. "Self-Report" in APA, "Self-report" in
AP and Chicago.
- The first word after a colon is capitalised, which AP and Chicago also do, so this is not a
difference so much as a rule all three share and people forget.
If you have picked AP and occasionally need APA, the practical delta is hyphens.
Sentence case, which is what most platforms use
The fourth option is not a title case at all: capitalise the first word and proper nouns, and nothing else.
It is worth taking seriously rather than treating as the lazy choice. Every major platform uses sentence case for its own interface text, most newsrooms outside the US have used it for headlines for decades, and it removes the entire question this post is about. It also has one real problem that no tool can solve for you: it cannot find a proper noun. "Turkey" the country and "turkey" the bird are the same string, and a converter that lowercases everything after the first word will quietly demote a brand name.
That is why a case tool should ask you for the names rather than guess, and why the sentence-case output is the one to read before copying.
Which to pick
There is no ranking answer, and the decision is smaller than the amount written about it.
Pick AP if you write anything news-adjacent, or if you want the rule that is easiest to apply without thinking — count the letters.
Pick Chicago if you publish long-form and want titles that look like book titles.
Pick sentence case if your titles are mostly questions and statements rather than labels, which on YouTube and in a newsletter they usually are.
Then keep it. The value of a title convention is consistency across a channel: a viewer scanning a grid registers inconsistent capitalisation as sloppiness long before they could tell you which guide you were following. Which guide you picked is something nobody has ever noticed.
What title case does not do
It does not affect ranking. No search engine treats capitalisation as a signal, and Google's guidance on titles is about what the title says rather than how it is cased.
What it affects is whether a title looks edited, which is a real effect on a human being reading a list of ten of them. And it affects width — capitals are wider than lower-case letters, so a title in title case is cut earlier than the same title in sentence case, which matters more than the style question does. YouTube title truncation covers where those cuts fall, and title case covers the mechanics of applying one.
What is the difference between AP and Chicago title case?
Prepositions of four letters or more. AP capitalises them - "Through", "Between", "Without" - and Chicago lowercases prepositions at any length. On a title with no long prepositions the two are identical.
Is APA title case the same as AP?
Nearly. APA uses the same four-letter rule, and adds that both halves of a hyphenated compound are capitalised. "Self-Report" in APA, "Self-report" in AP.
Which title case should I use?
Whichever you will apply consistently. AP is the easiest to apply mechanically, Chicago suits long-form, and sentence case suits titles that read as sentences. Nobody notices which; everybody notices inconsistency.
Does title case affect SEO?
No. No search engine treats capitalisation as a ranking signal. It affects how edited a title looks, and it affects width, because capitals are wider and get truncated sooner.
Paste a title into the title case converter and read the disagreement table — on most titles it is two words long.
Put it to work
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