Turnitin Similarity Score: What It Means and How It Is Calculated
Your Turnitin similarity score (also called the similarity rating or similarity percentage) is the share of your paper that matches text in Turnitin's databases. A 12% score means about 12% of your words match a web page, publication or another student's paper. It is not a plagiarism score, and it says nothing about AI writing. Here is how the score is worked out, what each range means, and what to do with yours.
How Turnitin calculates the similarity score
Turnitin compares your text with three collections:
- Internet: current and archived web pages.
- Publications: journals, books and conference papers.
- Submitted works: papers previously submitted by students at your institution and others.
It then adds up every word that belongs to a match and divides by the total words in your paper. If 300 of your 3,000 words match sources, your score is 10%. Each matched word is counted once, even if it matches several sources, which is why the source percentages do not always add up to the total.
What is and is not counted
| Text | Counted? |
|---|---|
| Uncited copied or closely paraphrased text | Yes |
| Quoted and cited text | Yes, unless your instructor excludes quotes |
| Reference list or bibliography | Yes, unless excluded (it usually is) |
| Small matches (for example under 8 words) | Only if your instructor has not filtered them |
| Your own earlier submission to another assignment | Yes, if it was stored in the repository |
Filters are set by your instructor. That is why the same paper can score 25% in one course and 9% in another. See why references raise your score.
Turnitin similarity score meaning by range
| Score | Colour | Usual reading |
|---|---|---|
| 0% | Blue | No matches. Fine, but check the report processed (see 0% similarity) |
| 1 to 24% | Green | Normal for a referenced paper, if no single source dominates |
| 25 to 49% | Yellow | Likely to be reviewed |
| 50 to 74% | Orange | High; usually needs explaining |
| 75 to 100% | Red | Very high (see 100% similarity) |
For a score-by-score breakdown, read Turnitin percentage meaning, 0% to 100%. For limits, read what Turnitin percentage is acceptable.
Why the score is not a plagiarism score
Turnitin finds matching text. It does not decide whether the match is plagiarism. A 20% score made of quoted, cited sentences can be perfectly acceptable. A 6% score made of one uncited paragraph from a classmate's paper is not. Your instructor looks behind the number at:
- The largest single source. Anything above roughly 5% from one source stands out.
- The match groups, especially "Not Cited or Quoted".
- Matches to submitted works, which can point to shared or reused papers.
Similarity score vs AI score
They are separate reports. The similarity score measures matching text. The AI writing score estimates how much of the prose reads as machine-generated. Our sample paper below scored 1% similarity and 51% AI. A low similarity score does not protect you from a high AI score.
A real similarity score next to an AI score
Both screenshots below come from the same 24-page, 6,364-word paper. The similarity report found 1% overall similarity. The AI writing report flagged 51% of the qualifying text as likely AI-generated. Tap either one to see it full size.
Screenshots shown for illustration. Your own reports arrive as full PDFs in your dashboard.
How to lower a high similarity score
- Fix every passage in the Not Cited or Quoted group: quote it and cite it, or rewrite it in your own structure and cite it.
- Add missing citations to quoted text.
- Replace long quotations with short quotes plus your own explanation.
- Check your reference list has a clear heading such as "References" so it can be excluded.
- Check again before you submit, so you are not relying on resubmissions.
Frequently asked questions
What is a Turnitin similarity score?
The percentage of your paper that matches text in Turnitin's databases of web pages, publications and student papers. It is not a plagiarism score.
How is the Turnitin similarity score calculated?
Turnitin adds up every word that belongs to a match and divides by the total words in your paper. Each matched word counts once.
What is a good Turnitin similarity score?
For most referenced coursework, under about 15 to 20% with no single source above roughly 5% is treated as normal.
Does the similarity score include AI?
No. AI writing is measured in a separate AI writing report.