What is a similarity score? (And what percentage is acceptable?)

When you run a document through a similarity checker, it compares your text against a large database of web pages, journal articles, books and other documents, and reports the percentage of your text that matches something else. That percentage is your similarity score (sometimes called a similarity index).

A similarity score is not a plagiarism verdict

This is the single most important thing to understand. Similarity software finds matching text; it cannot judge intent, quotation or citation. All of these count toward your score, and none of them are plagiarism:

• Quotations you have correctly marked and cited.
• Your reference list and bibliography (titles match the originals, naturally).
• Common phrases, standard terminology and methodological boilerplate ("data were analysed using…").
• Your institution's cover-page wording, declarations and templates.

Conversely, a low score does not guarantee innocence: a short, entirely copied paragraph can sit inside a long document and produce a small overall percentage while still being a serious problem. Always read the match list, not just the headline number.

So what percentage is acceptable?

There is no universal threshold, because every university, department and assignment sets its own rules. In practice:

• Under 10% is low for most purposes, and typical of well-cited original writing.
• 10–25% is common and usually acceptable if the matches are quotations, references and common phrases rather than copied argument.
• Over 25% deserves careful review before submission. It does not prove misconduct, but examiners will look closely.

Some institutions publish a hard limit (often around 20%, excluding bibliography and quotations). Your own institution's rule — not a number you read online — is the one that applies to you. Check your handbook, and when you check your document, use a report that excludes nothing you can hide behind: look at where the matches are.

How to lower a score legitimately

• Paraphrase properly: read the source, close it, write the idea in your own structure and words, then cite it. Swapping a few words ("patchwriting") still matches — and is still plagiarism.
• Quote sparingly and visibly: use quotation marks and a citation for anything you reproduce word-for-word.
• Summarise instead of stacking quotes: long chains of quotations inflate your score and weaken your argument.
• Check the match locations: one 8% block from a single source is far more worrying than forty 0.2% fragments.

Ready to see your own number? Check your document — you will see the word count and price before you pay, and your document is deleted as soon as your report is ready.