What Similarity Percentage Is Acceptable in Research Papers? (Practical Guide)
One of the most confusing questions in research writing is:
“What similarity percentage is acceptable?”
The honest answer is: there is no universal fixed number, but there are well-accepted academic standards. This article explains how similarity is judged in practice, not myths.
First, Understand What Similarity Really Means
Similarity tools (like Turnitin) measure text overlap, not plagiarism itself.
Similarity ≠ plagiarism
Context and source matter more than total %
Universities and journals look beyond the number.
Generally Accepted Similarity Ranges
Safe Range (Most Accepted)
Overall similarity: ≤ 15%
Single-source similarity: ≤ 3–5%
Usually accepted by:
SCI / Scopus journals
PhD thesis submissions
University evaluations
Borderline Range (Case-by-Case)
Overall similarity: 16–25%
May be accepted if:
Similarity comes from literature review
No single source exceeds limits
Proper citations are present
Methodology is original
Often leads to minor revision, not rejection.
High-Risk Range (Usually Rejected)
Overall similarity: > 25%
Single source: > 5–7%
Red flags:
Copied paragraphs
Methodology duplication
Self-plagiarism
Patchwork writing
Common outcome: rejection or resubmission required.
What Evaluators Actually Check
They focus on:
Single-source overlap (most important)
Copied sentence structure
Methodology originality
Self-plagiarism from earlier work
Whether similarity is justified and cited
A 12% paper can be rejected, and a 18% paper can be accepted—depending on content.
Common Myths
“Below 20% is always safe”
“Citations cancel similarity”
“0% similarity is ideal”
Truth:
Ethical writing + proper citation = acceptable similarity
Best Practice Recommendation
Aim for:
Overall similarity: ≤ 12–15%
Single source: ≤ 3%
Original writing in methods & results
This keeps you safe across most universities and journals.
Special Note for Theses
Many universities require:
≤ 10% for PhD thesis
≤ 15% for MPhil / Master’s
Always follow your university regulations first.
Conclusion
There is no magic similarity number, but 15% overall with low single-source overlap is widely accepted. What truly matters is where the similarity comes from and how ethically the content is written.
In one line:
Similarity is judged by quality and intent—not just percentage.