Key takeaways
- The similarity score is a text-matching percentage, not a plagiarism verdict.
- Filters and exclusions can change the number significantly.
- Acceptability depends on your institution, discipline, and how matches are cited.
The big red number at the top of a Turnitin report feels definitive, but it is only the starting point. Understanding what it measures—and what it ignores—helps you respond intelligently.
How the percentage is calculated
Turnitin divides the total matched text by the total document length. Every match counts, including properly quoted material unless you apply filters.
Colour codes and match sources
Each colour represents a different source. Click any highlight to see the matched text alongside the original. Long consecutive matches in your own prose without citations are the primary concern.
Using filters correctly
- Exclude bibliography to remove reference-list matches.
- Exclude quoted material to see only paraphrased overlap.
- Set a minimum word count to ignore common short phrases.
- Exclude small sources that add noise without meaning.
What is generally acceptable
Below 15% with no uncited verbatim passages is acceptable at most institutions. Literature-heavy chapters may run higher if every match is attributed. Above 25% with large uncited blocks is rarely acceptable anywhere.
What is never acceptable
Entire paragraphs copied from a source without quotation marks or citation. Purchased essays. Uncited patchwriting. These fail review regardless of the overall percentage.