APA vs. Chicago: differences and when to use each

APA vs. Chicago: which Chicago?

Comparing APA to "Chicago" requires a clarifying question, because Chicago is two systems sharing one manual:

Chicago author-date looks similar to APA — both use parenthetical author-year citations and a reference list. Chicago notes-bibliography uses footnotes and a bibliography, looking nothing like APA. This guide covers both comparisons.

APA vs. Chicago author-date

APA and Chicago author-date are the two leading author-date systems in academic publishing. They are visually similar but differ in a handful of conventions.

Three differences are immediately visible:

1. Author names. APA uses initials only ("Sampson, R. J."); Chicago uses full first names ("Sampson, Robert J.").

2. Year placement and punctuation. APA places the year in parentheses with a period: "(2012)." Chicago places the year directly after the author with a period: "2012."

3. Title capitalization. APA uses sentence case; Chicago uses headline case for book titles.

APA vs. Chicago notes-bibliography

Comparing APA to Chicago NB is comparing two fundamentally different citation philosophies. APA puts the citation in the text; Chicago NB puts it at the bottom of the page.

APA's in-text citation is fast for the reader to scan but limits how much commentary can ride along with the citation. Chicago NB's footnote can carry quotation, qualification, and translation alongside the citation — which is why historians prefer it.

Which to use when

Reference list vs. bibliography

APA and Chicago author-date both end with an alphabetized list under the heading References. Chicago NB papers end with a Bibliography — and the bibliography may include sources consulted but not cited, which APA does not allow.

Title capitalization and author names

APA uses sentence case throughout; Chicago uses headline case for book and journal article titles in both AD and NB forms.

APA uses initials for author first names; Chicago spells them out (when they appear in the source). This is the easiest visual marker for distinguishing the two.

DOIs and URLs

APA 7 requires DOIs as full URLs (https://doi.org/10.xxxx/yyyy) with no trailing period. Chicago accepts the same form. Both styles drop the older doi:10.xxxx/yyyy form. Chicago NB places the DOI at the very end of the note or bibliography entry, immediately preceded by a comma; APA places it on its own with no terminal punctuation.

Common mistakes when switching

Comma between author and year

APA puts a comma there: (Sampson, 2012). Chicago author-date does not: (Sampson 2012). Bringing the APA comma into a Chicago paper is the most common conversion error.

Sentence case in Chicago

Chicago uses headline case for both books and journal articles. Importing APA's sentence case is a common slip when reformatting a paper.

Wrong list heading

APA → References. Chicago AD → References. Chicago NB → Bibliography. Calling a Chicago NB list "References" is a clear style mismatch.

Summary