Almost everyone using Turnitin for the first time asks the same thing: what percentage is safe? The answer you will find online is usually "under 15%" or "under 20%" — and it does not really match how the tool was designed.
The similarity score is not a plagiarism score
Turnitin has always been explicit that the Similarity Report is a comparison tool, not a plagiarism verdict. What the system does is simple: it compares your document against web pages, previously submitted papers and academic publications, then marks where the text overlaps.
In other words, it tells you "these words appear elsewhere". Whether that overlap is legitimate citation or plagiarism is a judgement made by a person — your marker — not by the number.
A literature review at 30% similarity where every match is a properly attributed quotation can be completely fine. A paper at 8% with one unattributed 200-word passage is a real problem.
What the colour bands mean
Turnitin colour-codes the overall figure so it can be scanned quickly:
| Colour | Range | Usual reading |
|---|---|---|
| Blue | 0% | No text overlap detected |
| Green | 1% – 24% | Common range; still review each source |
| Yellow | 25% – 49% | Substantial overlap; worth a careful look |
| Orange | 50% – 74% | Extensive overlap |
| Red | 75% – 100% | Most of the text matches other sources |
Note that the colour is not a pass/fail line. It is a visual cue. Green does not mean cleared, and yellow does not mean guilty.
The three things actually worth checking
1. How much comes from one source
20% spread across 40 sources at 0.5% each is usually just standard academic phrasing and references. 20% where a single source accounts for 14% means one chunk of your paper leans heavily on one text — and that is the case worth fixing. The Match Overview panel ranks sources by contribution.
2. How long the continuous matches are
Three or four matching words in a row mean nothing. But 25+ words matching exactly with no quotation marks is, formally, a direct quotation written as if it were a paraphrase — even if you put a citation at the end of the sentence. This is the single most common honest mistake.
3. Which section the overlap sits in
Overlap in the Methodology is normal; standard procedures have standard descriptions. Overlap concentrated in your analysis, discussion and conclusion — the parts that are meant to be your own argument — is a different matter entirely.
Text that gets flagged for no good reason
- The reference list. Dozens of APA or MLA entries identical to every other paper can easily contribute 10% or more on their own.
- Correctly attributed quotations. Quotation marks and a citation do not stop the system marking them.
- Title pages, declarations, course codes. Identical across everyone in your cohort.
- Fixed disciplinary phrasing. Legal provisions, accounting standards, the standard sentence for a statistical test.
Turnitin can exclude the bibliography and exclude quotes. Turning those on usually drops the number noticeably, and that lower figure is much closer to "overlap that actually matters". One caveat: those settings are controlled on the instructor's side, so the number you see may not be the number they see.
How to genuinely reduce similarity
- Change the structure before the words. Swapping synonyms is the least effective thing you can do — Turnitin matches word sequences, so a few substitutions still match. What works is reading the source, closing it, and rebuilding the point in your own sentence structure.
- Quote when you should quote. Rather than mangling a canonical definition into an awkward paraphrase, use quotation marks and a page number. Properly quoted text is normal scholarship, not a problem.
- Increase the proportion that is yours. High similarity is often not because you copied, but because there is too little of your own analysis and the paper is mostly other people's points.
- Watch for self-matching. If an earlier assignment of yours went into the Turnitin repository, a new one may match your own old work. That is self-plagiarism, and plenty of institutions treat it as a breach.
Check it yourself before you submit
At most Hong Kong institutions the Turnitin submission box opens once, or the report is only released after the deadline — which means you usually find out after submitting, when it is too late to change anything.
Submitting through TurnCheckHK gives you the same similarity report and source list your marker sees, and our instructor account is set to No Repository, so it does not affect your real submission later. Fix what needs fixing, check again, and hand in knowing where you stand.