Both styles at once, because they disagree — and the difference shows up in more headlines than you would think.
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01 · one rule apart
A Trip With Friends in AP style; A Trip with Friends in Chicago. That single disagreement is the whole difference between the two.
AP capitalises prepositions of four letters or more; Chicago leaves every preposition lower case however long it is. Since with, from, into, over, about and between are ordinary words in ordinary headlines, the rule fires constantly — which is why two publications can title the same article differently and both be correct.
Everything else the two styles agree on, and most Title Case converters online silently pick one without saying which. This one shows both and tells you when they differ.
02 · side by side
Three of these six titles come out differently under the two styles. The other three are identical, which is the more common case — but the difference is not rare enough to ignore.
| Input | AP | Chicago |
|---|---|---|
| a trip with friends | A Trip With Friends | A Trip with Friends |
| notes from underground | Notes From Underground | Notes from Underground |
| a look into the future | A Look Into the Future | A Look into the Future |
| a tale of two cities | A Tale of Two Cities | A Tale of Two Cities |
| war and peace | War and Peace | War and Peace |
| the world we live in | The World We Live In | The World We Live In |
Highlighted rows are the ones where the two styles disagree.
03 · the rules
▸ first and last word
Always capitalised, whatever they are. "The World We Live In" keeps its final "In" capitalised even though "in" is a preposition, because it ends the title.
▸ articles
A, an and the stay lower case in the middle: "A Tale of Two Cities". Both styles agree.
▸ coordinating conjunctions
And, but, or, nor, for, yet, so stay lower case: "War and Peace". Both styles agree.
▸ short prepositions
Of, in, on, to, at, by, up — three letters or fewer — stay lower case in both styles.
▸ long prepositions
With, from, into, over, about, between. This is the only place the two styles disagree, and it is why a converter has to pick one or show both.
▸ after a colon
The word after a colon is capitalised regardless: "The End: A Beginning".
The first rule beats all the others. "The World We Live In" ends on a preposition and capitalises it anyway, because it is the last word. The same goes for a title that opens with "The" or "A" — the article is raised because of where it sits, not because of what it is.
04 · the other styles
Title Case is one option among several, and the others are not wrong — they belong to different kinds of document. Knowing which is which saves an argument in a style meeting.
▸ Title Case
The important words raised, the small ones left down: "A Tale of Two Cities". Standard for headlines and book titles in American publishing, and what this page converts to.
▸ Sentence case
Only the first word and proper nouns: "A tale of two cities". The norm in British publishing, in user interfaces, and in almost all technical documentation. It is also easier to write consistently, because it needs no word list.
▸ Start Case
Every word raised, small ones included: "A Tale Of Two Cities". Common in slide decks and menus, and generally considered sloppy in prose — it is what a converter produces when it does not know the rules.
▸ ALL CAPS
Reserved for very short labels. Anything longer reads slowly, because the shape of a word is part of how it is recognised, and capitals flatten every word into the same rectangle.
The practical advice is unglamorous: sentence case is the safer default for a website, because it never needs a decision. Title Case reads as more formal and more editorial, and it costs a style choice on every heading — which is exactly the choice this page exists to settle.
05 · a note for other languages
Spanish and Portuguese titles use sentence case: the first word, proper nouns, nothing else. "Cien años de soledad", not "Cien Años De Soledad". So does French, and so does most of Europe.
This makes Title Case one of the clearest markers of a text written in English rather than translated into it — and, in the other direction, one of the most common mistakes when an English speaker writes a Spanish headline. If you work across the two, the rule is simply that the whole apparatus on this page applies to one of them and not the other.
The same asymmetry runs through months, weekdays and nationalities, which English capitalises and Spanish and Portuguese do not.
06 · questions
Q01
The convention of capitalising the important words in a heading and leaving the small ones lower case: "A Tale of Two Cities". It is not the same as capitalising every word, which is a different style sometimes called Start Case, and it is not sentence case, where only the first word is raised.
Q02
One rule: prepositions of four letters or more. AP capitalises them — "A Trip With Friends" — and Chicago does not — "A Trip with Friends". Everything else the two styles agree on. It sounds trivial until you realise it changes a large share of real headlines.
Q03
Whichever your publication uses, and if there is no house style, pick one and stay with it. AP is common in journalism and news writing; Chicago dominates in books and academic publishing. Neither is more correct, and mixing them within one site is the only actual error.
Q04
Not in the middle, in either style — it is short enough that AP and Chicago agree. "Back to the Future", not "Back To the Future". The exception is the usual one: if it starts or ends the title, it is capitalised.
Q05
Both halves are capitalised in a title: "The Twenty-First Century", "A Well-Known Problem". Some older style guides lowercase the second half when it is a suffix or a very minor word, but the modern convention in both AP and Chicago is to raise both.
Q06
They keep their capitals. This converter leaves a word alone if it is already in capitals and longer than one letter, so NASA stays NASA rather than becoming Nasa. The exception is text pasted entirely in capitals, which is treated as text to reformat rather than as a string of acronyms.
Q07
It depends on the design rather than on grammar. Title Case reads as more formal and is common in American publishing; sentence case is the norm in British publishing, in most user interfaces, and in almost all technical documentation. Both are defensible; consistency across the site is what matters.
Q08
Treat it as ordinary text in the middle of the title: a small word stays small. The only positions that force a capital are the very start, the very end, and the word after a colon. A dash does not reset the rule, which surprises people who expect it to behave like a colon.
Q09
Yes, always. Every form of the verb to be counts as a main word, however short: "This Is It", "How to Be Alone". They look like small words and they are not, which is one of the more common slips when capitalising by hand rather than with a converter.
Q10
Not really, and that is worth knowing if you write in more than one. Both use sentence case for titles — only the first word and any proper nouns are capitalised — so a Spanish headline written in English Title Case looks distinctly translated. The same goes for months and weekdays, which are lower case in both languages.
AP for news, Chicago for books, either one for anything else. The converter above shows both so you can see which one your house style has been using without knowing it.