How to Cite a Preprint from arXiv or bioRxiv

Preprints – research posted to arXiv, bioRxiv, or a similar server before formal peer review – show up constantly in coursework now, sometimes because the peer-reviewed version doesn’t exist yet, sometimes because the preprint version is faster to access than a paywalled journal record. Citing one correctly means naming the server where a journal name or publisher would normally sit, and showing that the work hasn’t been peer-reviewed.

Why the Disclosure Matters

A peer-reviewed article has been checked by independent experts before publication; a preprint hasn’t. That’s not a reason to avoid citing preprints – in fast-moving fields, the preprint is often the only available version of the most current work – but your reader needs to know which one they’re looking at. Every major style has a mechanism for this disclosure, whether it’s a bracketed descriptor, a plain-text note, or the server name or arXiv number on its own. Skipping it doesn’t make the source more credible; it hides information your reader needs to weigh the claim appropriately.

The Example Preprint

We’ll cite this preprint in every style:

• Author: Sebastian Ruder
• Title: An Overview of Gradient Descent Optimization Algorithms
• Server: arXiv
• Year: 2016
• arXiv ID: 1609.04747
• DOI: 10.48550/arXiv.1609.04747

APA 7th Edition

Ruder, S. (2016). An overview of gradient descent optimization algorithms. arXiv. https://doi.org/10.48550/arXiv.1609.04747

Key rules:

• The pattern comes from APA Style’s preprint article examples (Publication Manual section 10.8).
• Author formatted like any other reference: last name, initials.
• Title in sentence case and in italics, as for any stand-alone work.
• Server name (arXiv) in plain text after the title, where a publisher would normally go.
• APA’s examples carry no [Preprint] descriptor and no version number. The server name shows the source type.
• APA says to cite the final published version when you can, and the preprint when that is the version you used.

MLA 9th Edition

Ruder, Sebastian. “An Overview of Gradient Descent Optimization Algorithms.” arXiv, 2016, https://doi.org/10.48550/arXiv.1609.04747. Preprint.

Key rules:

• Author inverted (Last, First), same as any other MLA entry.
• Title in quotation marks, title case.
• The server (arXiv) sits in the container slot, in italics, as the repository CORE does in the MLA Style Center’s example.
• “Preprint.” ends the entry, in the optional-element slot. The Style Center’s post on working papers says a preprint is a kind of working paper and ends its example with “Working paper.”
• That post relates to the eighth edition of the MLA Handbook. This guide did not read the ninth edition’s text, so the label is the Style Center’s pattern, not a quoted rule.

Chicago 18th Edition (Notes and Bibliography)

Chicago 18 covers preprints in section 14.76, “Journal article preprints.” The manual’s text sits behind a paywall, so the forms below follow two university guides written for the 18th edition: Mendocino College’s and Monash University’s. They give the same pattern. The University of Portland’s guide sums up section 14.76: give “preprint” and the server name where a journal’s volume or issue would go.

Footnote:

1. Sebastian Ruder, “An Overview of Gradient Descent Optimization Algorithms,” preprint, arXiv, September 15, 2016, https://doi.org/10.48550/arXiv.1609.04747.

Bibliography entry:

Ruder, Sebastian. “An Overview of Gradient Descent Optimization Algorithms.” Preprint, arXiv, September 15, 2016. https://doi.org/10.48550/arXiv.1609.04747.

Key rules:

• In both guides, “preprint” comes right before the server name. In the note the commas set it off and it is lowercase. In the bibliography entry “Preprint” opens a new sentence, so it is capitalized.
• Both guides write the full date, for example “October 17, 2023” (Mendocino) and “September 4, 2022” (Monash). The example uses arXiv’s date for version 1, 15 September 2016, which matches the 2016 year in the other styles.
• arXiv lists version 2 of this paper on 15 June 2017. Neither guide says which date a revised version takes, so ask your instructor if you read version 2.
• Both the note and the entry end with the DOI link.
• For the manual’s exact wording, read section 14.76 in the Chicago Manual of Style Online.

Harvard

Ruder, S. (2016) ‘An overview of gradient descent optimization algorithms’, arXiv [Preprint]. Available at: https://doi.org/10.48550/arXiv.1609.04747.

Key rules:

• Cite Them Right sits behind a login, so this line follows two UK library guides built on it: De Montfort University’s and Reading’s. Both write [Preprint] after the italic name of the journal the paper will appear in (“To be published in Journal [Preprint]”).
• Neither guide shows a preprint that has no journal, so this line puts the server in the journal’s place. Your department’s guide has the last word.
• Titles in single quotation marks, as in both guides’ examples.
• Both guides end with “Available at:” and a plain address, then “(Accessed: date)” with the day you read the preprint. De Montfort says to use the DOI in place of the address when the paper has one.
• Our Harvard guide drops the access date after a DOI, because the DOI is permanent. That is why the line above has none.
• De Montfort’s other form uses the plain address and keeps the date: Available at: https://arxiv.org/abs/1609.04747 (Accessed: 20 October 2026). Use the one your department names.

IEEE

[1] S. Ruder, “An overview of gradient descent optimization algorithms,” 2016, arXiv:1609.04747.

Key rules:

• Initials before last name, matching every other IEEE reference.
• The year, then the arXiv number in italics, ends the reference. The IEEE Reference Guide gives this form under “Preprint arXiv”: J. K. Author, "Title of paper," year, arXiv number.
• The Guide’s example has no [Preprint] descriptor, no DOI and no “Available:” line. The arXiv number shows the source type.
• The Guide’s note on early-access articles says to cite the publisher’s version, not the arXiv version, once the publisher has it online.

Vancouver

1. Ruder S. An overview of gradient descent optimization algorithms. arXiv:1609.04747v1 [Preprint]. 2016 [cited 2026 Oct 20]. Available from: https://arxiv.org/abs/1609.04747v1

Key rules:

• No periods in the author initial (Ruder S).
• NLM’s Samples of Formatted References (item 34, “Forthcoming and Preprints”) put the server and the identifier after the title. Then comes [Preprint], where the journal block of a published article would go.
• arXiv’s reference page asks for the identifier as arXiv: plus the number, with no spaces.
• The samples add the year, the date you read it in brackets ([cited 2026 Oct 20]) and an “Available from:” line. The arXiv sample gives the abstract page’s address, not the DOI.
• NLM’s arXiv sample names the version in the identifier (arXiv:1702.01006v1) and gives an address without it. This line names version 1 in both places, an adaptation of arXiv’s advice to add the version to the identifier. The paper’s first version carries the 2016 date.

Quick Comparison Table

bioRxiv and Other Servers

APA’s preprint examples say to follow the same format for other preprint archives, and the other styles take the server’s name in the same place. The one difference worth knowing is the DOI. bioRxiv and medRxiv DOIs use the prefix 10.1101 rather than arXiv’s 10.48550. A different registration agency issues them: Crossref for bioRxiv, DataCite for arXiv. In APA, a bioRxiv preprint on soil microbiome resilience by Jackson W. Sorensen and Ashley Shade reads:

Sorensen, J. W., & Shade, A. (2019). Dormancy dynamics and dispersal contribute to soil microbiome resilience. bioRxiv. https://doi.org/10.1101/730283

And in Vancouver, common in the biomedical fields bioRxiv serves. NLM’s bioRxiv sample writes the server as “BioRxiv” and gives the preprint’s six-digit number. For a DOI assigned before 11 December 2019, that number is the end of the DOI:

1. Sorensen JW, Shade A. Dormancy dynamics and dispersal contribute to soil microbiome resilience. BioRxiv 730283 [Preprint]. 2019 [cited 2026 Oct 20]. Available from: https://doi.org/10.1101/730283

Citing Medicine (chapter 14, “Manuscripts and Preprints”) ends the same sample with the DOI link: Available from: https://doi.org/10.1101/069187. NLM’s samples page ends it with the preprint’s page on bioRxiv. The DOI link opens that page.

For how the platforms expect to be cited, see arXiv’s reference page. It sets the arXiv: identifier form. The citation paragraph of bioRxiv’s about page says to cite a preprint by its DOI.

Special Cases

Citing Preprint Comments

Some servers, including bioRxiv, let readers add public comments to a preprint’s page. Citing the discussion rather than the preprint’s findings? Treat the comment as its own dated source. Do not fold it silently into a citation of the original paper. No source behind this guide prints a form for a server comment, so ask your instructor which one fits.

The Preprint Was Later Published

If the work you read as a preprint has since been published in a peer-reviewed journal, cite whichever version you actually read. APA Style puts it this way: ideally, use and cite the final, published version, and if you used the preprint, cite that version. The Sorensen and Shade preprint above is an example. Crossref records that it was later published in a journal, so the published version has its own reference:

Sorensen, J. W., & Shade, A. (2020). Dormancy dynamics and dispersal contribute to soil microbiome resilience. Philosophical Transactions of the Royal Society B: Biological Sciences, 375(1798), 20190255. https://doi.org/10.1098/rstb.2019.0255

If you read the preprint but know the published version exists, your formal citation still points to the version you used. Naming the published version in your text helps the reader find it, though no style requires that. If you can read the published version, cite that one instead.

Citing a Specific Preprint Version

Preprint servers often host multiple revisions of the same paper (v1, v2, v3). If the version matters to your argument, name it. An earlier version may have made a claim the author later corrected. arXiv’s reference page says to add the version to the identifier (arXiv:1609.04747v1). That points readers at one version. bioRxiv’s about page says a revised version keeps the DOI of the first. Only a version-specific address then names the version you read. APA’s preprint examples show no version. For a dataset, APA puts the version in parentheses after the title, as our how-to-cite-a-dataset guide shows.

The Preprint Links to a Code or Data Repository

Many preprints, especially in computational fields, include a data-availability or code-availability statement pointing to a separate repository. If you’re citing that repository as its own source rather than only the paper describing it, see our guide on how to cite software and code for the version and descriptor rules that apply there.

Common Mistakes

1. Citing a preprint without showing its review status. Every style has a way to flag it, whether a descriptor or the server name – use it, since a reader assumes peer review unless told otherwise.
2. Confusing the arXiv and bioRxiv DOI prefixes. They resolve through the same doi.org system but different registration agencies issue them: DataCite for arXiv and Crossref for bioRxiv.
3. Citing the wrong version after the paper has been revised. Match your citation to the version you actually read.
4. Treating a preprint the same as a conference paper. They’re different source types with different disclosure needs – see our guide on how to cite a conference paper if that’s what you’re actually citing.

Try It with CiteTools

Paste an arXiv or bioRxiv DOI into CiteTools.io and CiteTools looks up its record and formats the reference in any supported style. The DOI to APA converter reads an arXiv DOI from DataCite and writes the APA entry, with the server name where the publisher would sit. Check the result against the forms above, because styles differ on how they show a preprint. For the arXiv DOI above, CiteTools prints “Version 2” in its APA, MLA and Chicago results. That DOI opens the second version of the paper. Its Harvard result has no [Preprint] label and no italics, and its MLA result has no “Preprint.” at the end. Add those by hand. The forms above leave the version out unless it matters (see Citing a Specific Preprint Version).

For a bioRxiv DOI, CiteTools currently prints three forms that differ from the ones above. APA gives a plain title and “In bioRxiv. openRxiv.” after it. Chicago gives “In bioRxiv. Preprint, openRxiv, August 8, 2019.” MLA gives “bioRxiv, openRxiv, 8 Aug. 2019” with no “Preprint.” Rewrite each result to match the forms above.

For a PubMed-indexed paper instead of a preprint server, see our guide on generating citations from a PMID. Collecting preprints alongside published articles for the same project? Our guide to converting citations between styles shows how to add several sources to one list.