Chicago author-date style is the version of Chicago referencing used in the sciences and social sciences. You cite the author's surname and the year in brackets, and list full details in a reference list at the end.
This page follows the 18th edition of the Chicago Manual of Style, published in 2024, and notes where it differs from the 17th. It covers in-text citations, the main reference formats, how Chicago compares with APA and a worked example.
Chicago Author-Date in Four Rules
- Cite in the text as (Surname Year), with no comma between name and year, adding a page number after a comma when needed.
- List every cited source in a reference list, alphabetical by first author's surname.
- Put the year straight after the author names in each reference entry.
- Use full first names, headline-case titles, quotation marks for article titles and italics for book and journal titles.
In-Text Citations
Author-date citations are short and sit inside the sentence, usually before the full stop. Their form depends on the number of authors.
| Situation | Example |
|---|---|
| One author | (Grant 2021) |
| Two authors | (Patel and Okafor 2023) |
| Three or more authors (18th edition) | (Moreno et al. 2022) |
| Specific page | (Grant 2021, 87) |
| Two sources together | (Grant 2021; Moreno et al. 2022) |
| Author named in the sentence | Grant (2021) argues that... |
| Same author, same year | (Osei 2020a, 2020b) |
The 17th edition listed all names for three authors in the text and used "et al." only from four authors. The 18th edition uses "et al." from three authors. Check which edition your course requires.
Journal Articles
Surname, First Name, and First Name Surname. Year. "Article Title in Headline Case." Journal Name Volume (Issue): pages. https://doi.org/xx.xxxx.
Patel, Ravi, and Ngozi Okafor. 2023. "Home Walking and Resting Blood Pressure in Older Adults." Journal of Applied Physiology Studies 15 (2): 101–9. https://doi.org/10.1000/japs.2023.0142.
- Invert only the first author's name; later authors appear first name first.
- Put the article title in quotation marks and headline case.
- Italicize the journal name, written in full; the volume number is not italic.
- Give the DOI as a full URL where one exists.
In the 18th edition, list up to six authors in the reference entry. For seven or more, list the first three followed by "et al." The 17th edition listed up to ten.
Books and Chapters
The 18th edition makes the place of publication optional, so most entries give only the publisher. Many courses still accept the place if you include it consistently.
Book: Surname, First Name. Year. Book Title in Italics. Publisher. Chapter in an edited book: Surname, First Name. Year. "Chapter Title." In Book Title, edited by First Name Surname and First Name Surname, pages. Publisher.
Grant, Helen. 2021. Clinical Pharmacology for Nurses. Northfield Press.
Osei, Kwame. 2020. "Renal Handling of Drugs." In Principles of Clinical Pharmacology, edited by Tom Ward and Amy Bell, 145–68. Northfield Press.
Chicago shortens page ranges, so 145 to 168 becomes 145–68 and 101 to 109 becomes 101–9. Use an en dash between the numbers in the reference itself.
Websites and Online Documents
Web pages follow the same author-year pattern. If no person is named, the organization becomes the author.
Organization or Surname, First Name. Year. "Page Title." Website Name. Month Day, Year. URL.
Northfield Health Trust. 2024. "Managing High Blood Pressure at Home." Northfield Health Trust. May 4, 2024. https://www.example.org/blood-pressure.
If the page has no date, use "n.d." in place of the year and add an access date, such as "Accessed October 2, 2026." Chicago otherwise does not require access dates.
Citing Figures, Tables and Specific Parts
To point to a particular figure, table or equation in a source, add it after the year, as you would a page number. This is common in science writing, where you reuse data or adapt a diagram.
(Patel and Okafor 2023, fig. 3)
(Grant 2021, table 4.2)
(Osei 2020, 152, eq. 7)
If you reproduce or adapt a figure, say so in your caption, such as "Adapted from Patel and Okafor (2023, fig. 3)", and make sure the full source is in the reference list.
Chicago Author-Date Versus APA
| Feature | Chicago author-date | APA 7th |
|---|---|---|
| In-text citation | (Grant 2021, 87) | (Grant, 2021, p. 87) |
| Author names in list | Full first names | Initials only |
| Year in list | After authors, no brackets | After authors, in brackets |
| Article titles | Headline case, in quotation marks | Sentence case, no quotation marks |
| Journal volume | Not italic | Italic |
A Worked Example
Text. Supervised walking lowered resting systolic pressure in older adults (Patel and Okafor 2023), though dropout was high in community settings (Moreno et al. 2022). Dose adjustment matters when kidney function is reduced (Osei 2020, 152).
References.
Moreno, Lucia, Yan Chen, and David Hart. 2022. "Adherence to Exercise Prescriptions in Primary Care." Primary Care Research Review 8 (4): 233–40. https://doi.org/10.1000/pcrr.2022.088.
Osei, Kwame. 2020. "Renal Handling of Drugs." In Principles of Clinical Pharmacology, edited by Tom Ward and Amy Bell, 145–68. Northfield Press.
Patel, Ravi, and Ngozi Okafor. 2023. "Home Walking and Resting Blood Pressure in Older Adults." Journal of Applied Physiology Studies 15 (2): 101–9. https://doi.org/10.1000/japs.2023.0142.
The authors, journals and DOIs here are invented to show the format. The list is alphabetical by first author, and each entry uses a hanging indent in a real document.
Formatting the Reference List
- Title the list "References" (author-date) and start it on a new page if your course asks for that.
- Order entries alphabetically by the first author's surname.
- List several works by the same author in date order, oldest first; add a, b and so on for the same year.
- Use a hanging indent, with each entry's second and later lines indented.
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Frequently Asked Questions
Most science and social science courses use author-date. Notes and bibliography is more common in history and the humanities.
The 18th edition, published in 2024. Some courses still use the 17th, so check your handbook.
No. Chicago author-date writes (Grant 2021). The comma comes only before a page number: (Grant 2021, 87).
In the 18th edition, use it in the text for three or more authors. In the reference list, name up to six authors; for seven or more, name the first three and add et al.
Only when the page has no publication or revision date. Otherwise the date of the page is enough.
Not in the 18th edition, which makes it optional. The 17th edition expected it, so follow the edition your course uses.