Direct answer
A 20% Turnitin similarity score is not automatically "too high," because Turnitin itself does not publish a universal pass/fail threshold [1]. Whether 20% is a problem depends on your institution's policy, the nature of the matched text (quotes, references, and common phrases all count), and the assignment type [2]. For most coursework, 20% falls in the "review your matches" zone rather than the "academic misconduct" zone, so your next step is to open the similarity report and inspect what was actually flagged before you decide to rewrite anything [4].
What Does a 20% Similarity Score Actually Mean?
The similarity score measures the percentage of your document that matches text in Turnitin's databases, which include published sources, web pages, and previously submitted student papers [2]. It is not a plagiarism percentage and it does not tell you that 20% of your work was copied — it simply reports that 20% of your text overlaps with something Turnitin can see [2].
A large share of that 20% often comes from legitimate material: your reference list, correctly cited direct quotes, assignment prompts, and standard academic phrasing. Because every match is counted mechanically, two students can both receive 20% for very different reasons — one with fully cited sources and another with uncredited copying [2].
The most useful information is not the headline number but the match breakdown underneath it. Turnitin groups overlaps by source and shows you which sources contributed the most, so you can judge whether the overlap is defensible before treating the score as a problem [2].
What Similarity Percentage Is Considered Acceptable by Universities?
There is no single acceptable percentage that applies everywhere, because each institution — and often each department — sets its own guidance [3]. In practice, many universities treat a range around 15–25% as acceptable for typical coursework, while they apply stricter expectations to dissertations, theses, and papers where original analysis is the core requirement [3].
Rather than memorizing a number, look for the stated policy in your module handbook or ask your instructor directly. Some markers flag reports above 20–25% for review, while others allow 30–40% when the matches are legitimately quoted sources [3].
The type of assignment matters as much as the threshold. A literature review or a law essay that relies on quotations will naturally score higher than an original lab report, so the same 20% can be perfectly fine in one context and concerning in another [3].
If your score sits close to your institution's cutoff, the fix is usually straightforward: paraphrase more aggressively, trim unnecessary quotes, and use the report's filters to confirm that the remaining matches are correctly cited rather than accidental overlap [3].
How Can I Check Which Parts of My Paper Are Flagged Before I Submit?
Open your similarity report and look at the color-coded highlights, which show every segment of your text that matches an external source [4]. Review the match list to see each contributing source and the percentage it represents, then click through the highlights to decide whether each overlap is a legitimate citation or something you should rewrite [4].
Use the report's exclusion filters to remove quoted material and the bibliography from the calculation, which gives you a clearer view of the similarity that actually comes from your own wording. If most of the 20% disappears once quotes and references are excluded, your score is almost certainly not a problem [4].
Check your report before the final submission deadline rather than after, because the point of a pre-submission check is to have time to act. If genuine copied passages or weak paraphrases are driving the score, revise those sections and run the check again so your submitted version reflects the clean result [4].
Before you submit and hope for the best, the fastest way to settle the "is 20% too high?" question is to see exactly what Turnitin flags on your own draft — in the same report format your professor sees. Turnitin0 gives you a real Turnitin similarity and AI report on your file within minutes, so you can confirm that your 20% is just quotes and references — or catch and fix the flagged passages before they cost you marks.
※ Turnitin0.com - Actual Turnitin AI Report Cover, Score, Flag And Similarity Summary
FAQ
Is a 20% similarity score bad?
Not by itself. A 20% score is common and is usually acceptable when the matches come from correctly cited quotes and references, but you should always review what was flagged rather than judging the number alone [2][4].
What percentage on Turnitin is considered plagiarism?
No specific percentage defines plagiarism, because the similarity score only measures text overlap [1]. Markers look at which sources were matched and whether the overlap is properly cited, not at a cutoff number in isolation [3].
Does my reference list count toward the similarity score?
Yes. Reference lists, bibliographies, direct quotes, and common headings all count toward the total, which is why so many reports land near 20% even for fully original work [2].
Can I lower a 20% similarity score?
Usually yes. Paraphrase rather than quote long passages, trim unnecessary citations, and use the report's exclusion filters to see how much real overlap remains after quotes and the bibliography are removed [4].
Do all universities use the same 20% threshold?
No. Thresholds vary by institution, department, and assignment type, so check your course handbook or ask your instructor for the specific guidance that applies to you [3].