AP vs. Chicago style: differences, examples and when to use each

AP style is the set of writing and editing rules published by The Associated Press in the AP Stylebook, the standard reference for U.S. news writing. Chicago style is the set of rules in The Chicago Manual of Style, published by the University of Chicago Press; the 18th edition came out in September 2024. This page compares the two rule by rule. For the full AP rule set, see the AP style guide. Examples are invented.

When to use AP and when to use Chicago

If an editor or publisher gives you a style sheet, that wins over both.

AP vs. Chicago: the side-by-side table

The differences that cause the most corrections

Commas

AP: The council approved the budget, the levy and the contract. Chicago: The council approved the budget, the levy, and the contract.

AP still uses the comma before "and" in a complex series ("toast, and ham and eggs") and wherever leaving it out would confuse. Chicago uses it every time.

Numbers

AP: The team has 12 players, nine of them from Ohio. She is 45. Chicago: The team has twelve players, nine of them from Ohio. She is forty-five.

Chicago's 18th edition added more guidance on when numerals are always used, and allows numerals for ages, centuries and similar items when many appear together. In news copy, AP's "10 and up" rule is simpler and saves space.

Percent

AP: Turnout fell 4%. Chicago (general writing): Turnout fell 4 percent.

AP switched from "percent" to the % sign in 2019. Chicago keeps "percent" in nontechnical prose.

Dates and times

AP: The hearing is at 9 a.m. Sept. 14 in Room 210. Chicago: The hearing is at 9:00 a.m. on September 14 in Room 210.

AP orders time, date, place and drops "on" when it isn't needed. Chicago writes the month out.

Possessives

AP adds only an apostrophe to a singular proper name ending in s: "Ross' notes." Chicago adds 's: "Ross's notes."

Composition titles: books, movies and songs in AP vs. Chicago

"Book title AP style" is one of the most searched AP questions, and the answer surprises Chicago-trained writers.

AP's capitalization rule for titles: capitalize the principal words, including prepositions and conjunctions of four or more letters ("Gone With the Wind," "Of Mice and Men"). Capitalize "the," "a" or "an" only at the start of the title. Chicago's 18th edition renamed "headline style" to "title case" and now capitalizes prepositions of five letters or more (such as "Between" and "Through") in titles.

Citations: AP has none, Chicago has two systems

AP style has no citation format. A news story attributes in the text: who said it or published it, what kind of source it is, and enough detail for a reader to find it. Online, you add a link. There are no footnotes, no reference list and no parenthetical citations.

An AP-style in-text citation (fictional study):

Teens who slept fewer than seven hours a night were twice as likely to report anxiety, according to a 2024 study of 3,000 high school students published in the Journal of Adolescent Health Research. The study was led by Maria Chen, a psychologist at Riverbend University.

What to include in AP attribution:

1. The source's name and credentials on first reference.
2. The type of source (study, report, court filing, interview).
3. The publication or agency and the year.
4. A link online, to the original rather than a press release about it.
5. "Said" for people, "according to" for documents.

Chicago gives you two full systems. The notes and bibliography system is the one historians and book publishers use; author-date is common in the sciences and social sciences and in reports.

Chicago notes and bibliography (18th edition, fictional sources):

Footnote, first citation:
1. Maria Chen, Harbor Towns: A Social History (Riverbend University Press, 2023), 112.

Shortened note, later citations (the 18th edition prefers this to "Ibid."):
2. Chen, Harbor Towns, 115.

Journal article note:
3. Luis Ortega and Priya Nair, "Food Insecurity in Midsize Cities," Journal of
   Urban Policy 18, no. 2 (2024): 52, https://doi.org/10.0000/example.

Bibliography:
Chen, Maria. Harbor Towns: A Social History. Riverbend University Press, 2023.
Ortega, Luis, and Priya Nair. "Food Insecurity in Midsize Cities." Journal of
   Urban Policy 18, no. 2 (2024): 45–67. https://doi.org/10.0000/example.

Chicago author-date (18th edition, fictional sources):

In-text: (Chen 2023, 112)   (Ortega and Nair 2024, 52)

Reference list:
Chen, Maria. 2023. Harbor Towns: A Social History. Riverbend University Press.
Ortega, Luis, and Priya Nair. 2024. "Food Insecurity in Midsize Cities." Journal
   of Urban Policy 18 (2): 45–67. https://doi.org/10.0000/example.

In print, book and journal titles are italic; the code blocks above can't show italics.

Three 18th-edition changes to know if you learned Chicago from the 17th:

• No place of publication is needed for books: "(Riverbend University Press, 2023)," not "(Chicago: Riverbend University Press, 2023)."
• Shortened notes replace "Ibid." as the preferred form for repeat citations.
• "Et al." rules: in notes and author-date citations, list up to two authors; for three or more, give the first author plus "et al." In a bibliography or reference list, list up to six authors; for more than six, list the first three plus "et al."

Other styles writers meet

If you write research-based reports or reviews, the citation side matters more than the comma side. See our guide to AI literature review tools for building the source list behind a report.

Switching styles in one document

Writers who move between journalism and books often need both styles on the same material: a news story and a book chapter from the same reporting, or a press release about a report with a Chicago reference list. Change these in order:

1. Citations first. Convert AP attributions to Chicago notes or author-date references, or the reverse. This is the slowest part, so do it once, from a list of sources rather than by hand from the text.
2. Composition titles. Quotes to italics (AP to Chicago) or italics to quotes.
3. Numbers, percent, dates and times. Search for figures under 100, %, month abbreviations and :00.
4. Commas. Add or remove serial commas.
5. Titles and possessives. Gov. to Governor; Jones' to Jones's.
6. Dashes and ellipses. Change the spacing.

For steps 2 to 6, the AI prompt in our AP style checker comparison works as a converter: ask it to list every change in a table so you can approve each one.

How WriteOrbit handles the citation half

WriteOrbit manages citations, not AP prose rules. What it does:

• 10,000+ citation styles, including Chicago notes and bibliography, Chicago author-date, APA, MLA, IEEE and Harvard, through the CSL citation styles library.
• Switch a document's citation style in one step. Every in-text citation and the reference list reformat together, so a report drafted in APA can go to a Chicago publisher without retyping.
• Find papers and @-cite. Search 250M+ scholarly works from the editor and type @ to cite one; the citation is formatted in the document's style.
• Word in and out. Open a .docx, and export Word, PDF or a LaTeX project (LaTeX export is on paid plans).

What it doesn't do: change "5%" to "5 percent," add serial commas or italicize titles in your prose. Switching the citation style only changes citations. Use the converter prompt in the AI chat beside the document for the prose, and make those edits as tracked suggestions so an editor can review them.

Citations work in every style on the free plan; see pricing for current limits.

FAQ

What is the main difference between AP and Chicago style?

AP style is built for news: short forms, few commas, figures for 10 and up, and no citation system. Chicago style is built for books and long-form work: the serial comma, most numbers up to one hundred in words, italic book titles, and two full citation systems, notes and bibliography or author-date. Pick by publication, not by preference.

How do you cite sources in AP style?

AP style has no formal citation format. You attribute in the text: name the source, say what kind of source it is, and give enough detail for readers to find it, such as "according to a 2024 study in the journal Pediatrics." Online, link to the source. There are no footnotes, reference lists or parenthetical citations.

Are book titles italicized in AP style?

No. AP style puts book titles in quotation marks and capitalizes the principal words, including prepositions and conjunctions of four or more letters: "Gone With the Wind." AP doesn't italicize any titles. Chicago style italicizes book titles and uses quotation marks for shorter works such as articles, chapters, songs and poems.

Does Chicago style use the Oxford comma?

Yes. The Chicago Manual of Style recommends the serial (Oxford) comma in every series of three or more: "red, white, and blue." AP style leaves it out of a simple series and uses it only when an item contains its own conjunction or when leaving it out would cause confusion.

Which is used more, AP or Chicago?

They serve different markets. AP is the default for U.S. newspapers, broadcast news, wire services and most PR. Chicago is the default for U.S. book publishing and is common in history, the arts and some magazines. Academic writers in the sciences and social sciences more often use APA, and humanities students MLA.

Next step

If you write news most of the time, learn AP properly first: the AP style guide covers the 25 rules editors fix most. If your next project is a sourced report, see AI literature review tools for finding and organizing the sources you'll cite in Chicago.

Sources

1. The University of Chicago Press, "What's New in the 18th Edition," The Chicago Manual of Style Online: https://www.chicagomanualofstyle.org/help-tools/what-s-new.html
2. CMOS Shop Talk, "CMOS 18 Is Now Online" (Aug. 15, 2024): https://cmosshoptalk.com/2024/08/15/cmos-18-is-now-online/
3. The Chicago Manual of Style Online, Q&A on percent in nontechnical writing: https://chicagomanualofstyle.org/qanda/data/faq/topics/Abbreviations/faq0097.html
4. The Associated Press, AP Stylebook: https://www.apstylebook.com/
5. Purdue OWL, "AP Style": https://owl.purdue.edu/owl/subject_specific_writing/journalism_and_journalistic_writing/ap_style.html
6. ACES: The Society for Editing, "AP announces Stylebook changes; healthcare tops list" (2026): https://aceseditors.org/2026/04/24/ap-announces-stylebook-changes-healthcare-tops-list/
7. Poynter, "AP says the percentage sign is now OK when used with a numeral" (2019): https://www.poynter.org/reporting-editing/2019/ap-says-the-percentage-sign-now-ok-when-used-with-a-numeral-thats-shift5/
8. ACES, "AP Stylebook announces historic Merriam-Webster collaboration at ACES 2024": https://aceseditors.org/news/2024/ap-sylebook-announces-historic-merriam-webster-collaboration-at-aces-2024-san-diego