Turnitin Similarity Score for a Thesis: What Is Acceptable and Why

There is no single acceptable Turnitin similarity score for a thesis. Turnitin itself says “There is no fixed number” and that every school, instructor or assignment can accept a different amount of matching text. What matters is what each match is: a correctly quoted and cited source, your own reference list, or text that should not be there.

This guide explains what the Turnitin similarity score for a thesis measures and why long documents behave differently. It also covers checking before you submit, and how one university’s examiners are told to read the report. It ends with a self-review you can run on your own draft.

What the similarity score measures

The score is the share of your text that matches text in Turnitin’s database. It is not a plagiarism verdict.

Turnitin’s student guide is direct about this: “Turnitin does not check for plagiarism.” It compares your submission against its database. Turnitin says that database includes current and archived internet content, periodicals, journals and publications, and a repository of work other students have submitted (Turnitin, understanding the similarity score for students).

The same guide defines the similarity score as “the percentage of matched text your submission contains”. It adds that quotes and references used correctly will still be highlighted as matches. Turnitin’s product page puts it the same way for institutions: the tool flags text similarity “however, it does not determine whether plagiarism has occurred” (Turnitin Similarity).

What the colours mean

For classic assignments, the report icon’s colour follows the score. Turnitin lists these ranges:

• Blue: no matching text.
• Green: one word to 24% matching text.
• Yellow: 25 to 49%.
• Orange: 50 to 74%.
• Red: 75 to 100%.

Turnitin notes that the colour scheme can vary with the integration your university uses. A colour is a range, not a judgement.

Is there an acceptable similarity score for a thesis

No universal one. Your university’s regulations or your graduate school’s guidance decide.

Turnitin’s advice to students is to check the instructions, ask for the expected range, and read your institution’s policy on what counts as acceptable. De Montfort University’s guide for internal examiners says “There is no threshold figure for the similarity score which reliably indicates evidence of plagiarism or not” (De Montfort University, Turnitin guide for internal examiners).

The same guide adds that a figure below 20% is unlikely to indicate widespread plagiarism. But even that “does not discount the possibility of clear plagiarism in a small sub-section of the document.” In other words, a low number can still hide one copied paragraph, and a higher one can be mostly quotes and references.

Why thesis scores behave differently

Turnitin and De Montfort describe four situations that change what the number means.

1. Length can round small matches away. Turnitin says a document of considerable size can show a 0% score with a report that still contains matches. The score has been rounded to 0% rather than being exactly 0%.
2. Your own drafts can match you. If several drafts of the same paper go into your institution’s private repository, Turnitin says the final draft can score 100%. Its advice is to submit only the final draft to the repository.
3. Your own published papers can match you. De Montfort’s guide tells examiners that the first step with a match is to check the original source, to make sure the student is not its author.
4. Quotes and the reference list count. Correct quotations and bibliography entries still show as matches unless they are excluded.

What exclusions you can apply, and what they change

Turnitin’s student guide on exclusions says you can exclude quotes, the bibliography and small matches to get a more focused report (Turnitin, using exclusions and filters). The lowest small-match threshold is 8 words, which is the default setting.

The catch is in one line. As a student, any exclusions you make “are temporary, and will not reflect your official similarity score that your instructor sees.” If you think the official score should exclude your bibliography or quotes, Turnitin’s advice is to contact your instructor.

Can you check your thesis on Turnitin before submitting

Only if your university gives you a route. Turnitin’s help centre says a student cannot self-check a paper in Turnitin without uploading it to an official assignment created by an instructor, unless the institution has enabled Turnitin Draft Coach (Turnitin help centre).

The routes it lists:

1. Draft Coach, if your institution provides it. It runs similarity reports inside Google Docs or Microsoft Word.
2. An assignment that allows resubmissions. Each new upload overwrites the last. On classic assignments the first three attempts generate a report immediately, and after that you wait 24 hours. On the newer assignment type you get up to three resubmissions in a 24-hour period.
3. A practice assignment. If resubmissions are off, your first upload is final, and Turnitin suggests asking your instructor to set up a separate practice assignment.

If you want to check before submission, ask early, because at universities such as De Montfort the check runs as part of formal submission.

How one university’s examiners read the report

De Montfort University requires all research degree theses to be analysed using TurnitinUK when they are submitted for examination. Students upload the thesis within three days of submitting the written thesis to the Graduate School Office, and the internal examiner checks the similarity report.

The guide says TurnitinUK identifies any sequence of 7 words in the student’s text that matches a source. If a highlighted sequence runs to several sentences, the guide says it is “highly likely” the text was copied. If plagiarism is suspected and confirmed, the examination process is stopped. If the examiner is satisfied, the report goes to the external examiner with the internal examiner’s conclusion, or to the viva.

The useful lesson is what an examiner looks at: long runs of matched words, not the headline number.

A self-review before your thesis goes through Turnitin

You do not need Turnitin to find most problems a similarity report would show. Work through this on your final draft.

1. Search your draft for every quotation mark and check each quote has a citation and page number.
2. Check that long quotations use your style guide’s block format.
3. Read every paragraph built from one source and confirm it is cited, even where you paraphrased.
4. Mark any passage you took from your own earlier papers, reports or proposal, and follow your regulations on declaring it.
5. Check every secondary citation uses the “as cited in” form, as in our guide to secondary source citation in APA.
6. Check every reference exists and matches what you cite it for, using how to verify references.
7. If you used a writing assistant at any stage, check your university’s policy on declaring it. Our guide on using ChatGPT for your thesis covers what to look for in a policy.

For a full read-through method, see how to review your own thesis.

What Turnitin does well, and where this page stops

Turnitin compares your text against a large database of student submissions, publications and internet content and shows exactly where each match comes from, side by side with the source. De Montfort University, for example, builds it into research degree thesis submission.

What a similarity report cannot tell you is whether a match is acceptable. That is a judgement your examiners make, using your regulations.

What Thesisroom does with this

Thesisroom’s Citation Check room looks up every reference in your bibliography in published research databases such as Crossref and OpenAlex, checks whether the DOI resolves and whether the paper has been retracted. It does not rewrite your citations or generate replacement references. It checks your references, not how your wording matches other texts, so it does not replace a similarity report.

FAQ

What is an acceptable Turnitin similarity score for a thesis?

There is no universal figure. Turnitin says there is no fixed number and that each institution can accept a different amount. De Montfort University’s examiner guide says no threshold reliably indicates plagiarism. Check your own regulations.

Is 25% on Turnitin too high for a thesis?

Not on its own. In Turnitin’s classic colours, 25% is the start of the yellow band, but the colour is a range, not a verdict. What matters is whether the matches are correctly cited quotes and references or uncited text.

Does Turnitin check for plagiarism?

Turnitin’s student guide says it does not check for plagiarism. It compares your text with its database and highlights matches. Your examiners decide whether any match is a problem.

Can I check my thesis on Turnitin before submitting?

Only through your institution: Draft Coach if your university provides it, an assignment that allows resubmissions, or a practice assignment set up by an instructor. Turnitin’s help centre says students cannot self-check otherwise.

Do my own published papers count against my similarity score?

They can show as matches. De Montfort University tells examiners that the first thing to do with a match is to check the original source, to make sure the student is not its author.

Does excluding the bibliography change my official score?

Not if you do it yourself. Turnitin says exclusions a student makes are temporary and do not change the official score your instructor sees. Turnitin’s advice is to contact your instructor if you think exclusions should apply.

Sources

• Turnitin, understanding the similarity score for students
• Turnitin, using exclusions and filters
• Turnitin help centre, checking a paper for similarity before submitting
• Turnitin Similarity product page
• De Montfort University, Turnitin guide for internal examiners

How this guide was made: Thesisroom drafted this guide with the help of AI writing tools. Every fact, figure and source in this post was checked against its original source before publishing.