Citation and Referencing Guide: APA, MLA and Chicago
plagiarism-checker-online.net Editorial Team | Updated October 3, 2026
The short version: Cite whenever you use someone else's words, data or ideas. Use the style your course names, keep your sources organized while you read, and check every reference against the original before you submit. Citing correctly is the most reliable way to avoid plagiarism, and it is mostly a matter of habit.
Citation has two parts: a short pointer in your text and a full entry in your reference list. Together they let a reader find your source. This guide covers the decisions you make along the way and points to our detailed articles and free tools for each.
When You Need to Cite
You cite direct quotations, paraphrased ideas, specific facts and figures, images, and anything you reuse from your own earlier work. You usually do not cite common knowledge. A paraphrase still needs a citation, because the idea belongs to the source even if the words are yours.
- How to Cite Properly: APA, MLA and Chicago explains when citation is required and the mistakes students make most often.
- Paraphrasing vs. Plagiarism shows why rewording alone is not enough.
- How to Avoid Plagiarism places citation inside a wider workflow.
Choosing a Style
Styles are conventions that belong to fields. The names below are typical associations, not rules. Your instructor's choice always wins.
| Style | Often used in | In-text pointer |
|---|---|---|
| APA | Psychology, education, social sciences | Author and year |
| MLA | Literature, languages, humanities | Author and page |
| Chicago | History, arts, some humanities | Footnotes or author and year |
| Harvard | Varies by university, common outside the US | Author and year |
Citing Sources You Meet Every Day
Books, journal articles and websites make up most reference lists. The details that go wrong are small: the year, the DOI, the capitalization of titles and the order of authors. Collect these details when you read, not the night before the deadline.
- Our free Citation Generator formats books, articles and websites in APA 7, MLA 9, Harvard, and Chicago, can fetch details by DOI and exports to Word, RIS and BibTeX.
- The free Source Check compares up to 20 references with Crossref and marks each one as verified, partial or not found.
- The paid APA Citation Check compares APA 7 in-text citations with your reference list, from $0.19 per page. It never verifies that a source exists.
- When a reading points to a work you cannot retrieve, use the decision tree for citing a source you have not read before adding it to your reference list.
Annotated bibliographies
A formatted source entry doesn't make copied annotation text acceptable. Our annotated bibliography plagiarism guide shows how to write an original summary, evaluate the source and explain its use in your project.
Citing AI Tools
Generative AI is now part of the citation conversation. Style guides publish formats, and many instructors ask for a short disclosure in addition to the citation. The rules are new and change, so check the current guidance of your style and your course.
- How to Cite ChatGPT in APA, MLA and Chicago has copy-ready examples and in-text formats.
- The free AI Usage Statement tool builds a disclosure and usage log you can export.
- University AI Policies 2026 explains why the answer to "is this allowed" differs between courses.
Check Before You Submit
- Every in-text citation has a matching entry in the reference list, and the other way around.
- Quoted text is in quotation marks, with a page or paragraph number where your style requires it.
- Author names, years, titles and DOIs match the source, not a search result snippet.
- You formatted the list in one style, with consistent punctuation and ordering.
- A plagiarism scan shows no uncited matches. A scan will not tell you whether your format is right, only whether text overlaps with sources.
Check Your Paper for Missing Citations
A similarity report shows which passages match published sources, so you can add the citations you missed. Usually ready in about 15 minutes. No subscription.
Run a Plagiarism Check Free Tools See PricingFrequently Asked Questions
Which citation style should I use?
Use the one your instructor, department or journal names. If nothing is specified, ask. Styles are conventions for one field, so the right choice depends on your course, not on which one looks simpler.
Do I have to cite common knowledge?
Usually not, but what counts as common knowledge depends on your audience and field. If you needed to look a fact up, or the claim is a specific figure, finding or opinion, cite it. When in doubt, cite.
Do I need to cite ChatGPT?
If your course allows AI tools and you use the output or ideas from it, most style guides and instructors expect you to say so. Formats differ by style, and a separate AI usage statement is often required. See our article on citing ChatGPT for copy-ready examples.
Can a citation generator make mistakes?
Yes. Generators format the data you give them, so a wrong author, date or title produces a wrong citation. Always compare the result with the source and with your style guide, and verify DOIs and titles with a source check.