Title Capitalization Rules

There are two basic styles for the capitalization of titles and headlines, sentence case and title case.
In sentence case, the first word and all proper nouns and proper adjectives are capitalized. All other words are lowercased (just like in a regular English sentence): Bank of America is missing out on Wall Street’s boom
In title case, the first word (and usually the last word) is capitalized, as well as all major words. Minor words are lowercased: Bank of America Is Missing Out on Wall Street’s Boom
However, there is no universal convention which words in a title are major and which are minor. Rather, there are various style guides which each have their own rules regarding title case. This page describes the title case rules of six common style guides: the AP Stylebook, the APA Publication Manual, the Chicago Manual of Style, the MLA Handbook, the New York Times Manual of Style and Usage and the Wikipedia Manual of Style. Also featured is a table with a comparison of these styles.
A different approach to title case can be found on the page Words to Capitalize in a Title, which specifies the correct capitalization for individual words. And of course, the Title Case Converter offers a fully automatic conversion to title case, applying the rules of the style of your choice.

AP Title Case

  • Capitalize the first word and the last word of the title
  • Capitalize the principal words
  • Capitalize all words of four letters or more
  • Do not capitalize articles, conjunctions and prepositions of three letters or fewer

Source

Froke, Paula, Bratton, Anna Jo, Garcia, Oskar, McMillan, Jeff, Minthorn, David and Schwartz, Jerry. The Associated Press Stylebook and Briefing on Media Law 2018. New York: Basic Books, 2018.

Commentary

It should be noted that the rules above are the AP rules for composition titles (titles of books, movies, songs, poems etc.) For headlines, the AP Stylebook prescribes sentence case.
The AP title case rules are rather brief and leave several questions unanswered. For example, it is stated that conjunctions are not capitalized (unless they have four or more letters), but it is unclear whether this only refers to coordinating conjunctions or also includes subordinating conjunctions (e.g. if). The former seems more likely since this would be consistent with other style guides.
Furthermore, it is not specified whether to in infinitives should be capitalized or not. Since all other styles discussed on this page do not capitalize to in infinitives, it seems reasonable to assume the same for AP style.

APA Title Case

  • Capitalize the first word of the title and any subtitle
  • Capitalize verbs, nouns, adjectives, adverbs and pronouns
  • Capitalize all words of four letters or more
  • Do not capitalize articles, conjunctions and prepositions of three letters or fewer
  • Capitalize both words of hyphenated compounds
  • Capitalize the first word after a colon or dash
  • Do not capitalize the second part of a Latin species name

Sources

American Psychological Association. Publication Manual of the American Psychological Association. 6th ed. Washington, DC: American Psychological Association, 2010.
Lee, Chelsea. “Title Case and Sentence Case Capitalization in APA Style.” APA Style Blog. March 9, 2012. Accessed September 1, 2018. http://blog.apastyle.org/​apastyle/​2012/​03/​title-case-​and-​sentence-​case-​capitalization-​in-​apa-​style.html
McAdoo, Timothy. “How to Format Scientific Names of Animals.” APA Style Blog. February 15, 2017. Accessed September 1, 2018. http://blog.apastyle.org/​apastyle/​2017/​02/​-how-to-​format-​scientific-​names-​of-​animals.html

Commentary

While all other styles discussed on this page always capitalize the last word of a title, APA style has no such rule, which means that prepositions at the end of titles must be lowercased (e.g. “Service You Can Count on”).
The APA Publication Manual states that conjunctions should not be capitalized, but does not make a distinction between coordinating and subordinating conjunctions (just like the AP Stylebook). This raises the question how the subordinating conjunctions as and if should be handled in APA style. The fact that there are articles published in APA journals where if was capitalized in the title suggests that only coordinating conjunctions are lowercased in APA style whereas subordinating conjunctions are capitalized.
The APA Publication Manual also does not mention how to in infinitives should be handled, but again there are examples of actual applications, and they suggest that to in infinitives is lowercased in APA style.

Chicago Title Case

  • Capitalize the first and last words of titles and subtitles
  • Capitalize nouns, pronouns, verbs, adjectives, adverbs and some conjunctions
  • Do not capitalize articles and prepositions (regardless of length), except for prepositions that are part of Latin expressions used adjectivally or adverbially (e.g. “In Situ”)
  • Do not capitalize the conjunctions and, but, for, or and nor
  • Do not capitalize to in infinitives
  • Do not capitalize as in any grammatical function
  • Do not capitalize the part of a proper name that would be lowercased in text (e.g. “Vincent van Gogh”)
  • Do not capitalize the second part of a Latin species name, even if it is the last word of the title or subtitle
  • In hyphenated compounds, capitalize the first element and subsequent words that are not articles, prepositions, coordinating conjunctions or modifiers following musical key symbols (e.g. “Symphony in F-sharp Major”); however do not capitalize the second word if the first element is a prefix that could not stand by itself (e.g. “Ex-wife”), unless it is a proper noun or proper adjective.

Source

The Chicago Manual of Style. 17th ed. Chicago: University of Chicago Press, 2017.

Commentary

The title case rules of the Chicago Manual of Style are more exhaustive than all others, and they feature a few peculiarities: All other styles (except for the New York Times) lowercase all seven coordinating conjunctions, but only five are lowercased in Chicago style, namely and, but, for, nor and or, whereas yet and so are capitalized.
On the other hand, as is always lowercased in Chicago style, whereas all other styles (again except for the New York Times) capitalize as when used as subordinating conjunction.

MLA Title Case

  • Capitalize the first word and the last word of titles and subtitles
  • Capitalize nouns, pronouns, verbs, adjectives, adverbs and subordinating conjunctions
  • Do not capitalize articles, prepositions (regardless of length) and coordinating conjunctions
  • Do not capitalize to in infinitives
  • Capitalize principal words that follow hyphens in compound terms

Source

Modern Language Association of America. MLA Handbook. 8th ed. New York: Modern Language Association of America, 2016.

Commentary

MLA style is similar to Chicago style insofar as both lowercase all prepositions, regardless of length. However, MLA style has simpler rules regarding hyphenated terms, treats all coordinating conjunctions alike and does not have special rules for as and species names.

New York Times Title Case

  • Capitalize nouns, pronouns and verbs
  • Capitalize all words of four or more letters
  • Capitalize no, nor, not, off, out, so and up
  • Do not capitalize a, and, as, at, but, by, en, for, if, in, of, on, or, the, to, v., vs. and via, except when used as adverbs
  • Capitalize for if it takes the place of a verb meaning “support” or “advocate”
  • In hyphenated compounds, do not capitalize the second part if it follows a prefix of two or three letters and if the hyphen separates doubled vowels (e.g. “Co-operation”). Otherwise, capitalize the second part (e.g. “Co-Author”).

Source

Siegal, Allan M., Connolly, William G., Corbett, Philip B., and New York Times Company. The New York Times Manual of Style and Usage. 5th ed. New York: Three Rivers Press, 2015.

Commentary

The New York Times style is unique among the styles discussed here since not all 2- and 3-letter preposition are lowercased in this style. Instead, short words to capitalize and to lowercase are explicitly listed. This results in the prepositions off, out and up being capitalized in New York Times style while they would be lowercased in any other style.
Taken verbatim, the New York Times rules would mean that in and on should be lowercased when used as adjectives, but that is probably not the intended meaning, and evidence suggests that they are capitalized in that grammatical function.
Wikipedia logo

Wikipedia Title Case

  • Capitalize the first word and last word of the title
  • Capitalize verbs, nouns, pronouns, adjectives, adverbs and subordinating conjunctions
  • Capitalize prepositions of five letters or more
  • Capitalize the first word in a compound preposition (e.g. “Out of”)
  • Do not capitalize articles, prepositions of four letters or fewer and coordinating conjunctions
  • Do not capitalize to in infinitives
  • For hyphenated words, follow the majority usage in independent, reliable sources

Source

Wikipedia:Manual of Style/Titles#Capital_letters.” Wikipedia. Accessed September 1, 2018. https://en.wikipedia.org/​wiki/​Wikipedia:​Manual_of_Style/​Titles​#Capital_letters.

Commentary

In Wikipedia style, preposition with up to four letters are lowercased, which means that Wikipedia style represents a compromise between journalistic styles, where only short preposition with up to three letters are lowercased (e.g. AP) and academic styles, where all prepositions are lowercased, regardless of length (Chicago, MLA).
The Wikipedia rules are detailed and clearly specify how to capitalize a multitude of cases, with the exception of hyphenated compounds, for which the rules instruct to follow external sources. This seems unusual.

Style Guide Comparison

The following table provides a comparison of the title case rules of the six style guides supported by this website. The following symbols are used: stands for “capitalize,” stands for “lowercase,” and “” means that the style guide does not have a rule for the word or case in question.
AcademiaJournalism
CMOSMLAAPAAPNYTWP
first word
last word
nouns
pronouns
verbs
adjectives
adverbsas
but
to
other
articles
prepositions1 letterv.
2 lettersat
by
in
of
on
up
to
other
3 lettersbut
for /
off
out
via
other
4 lettersfrom
into
unto
with
other
5+ lettersany
coordinatingfor
conjunctionsand
nor
but
or
yet
so
subordinatingas
conjunctionsif
other
“to” in infinitives
second part of species names