100% Similarity on Turnitin: Why It Happens and What to Do
A 100% similarity score on Turnitin means every part of your paper matches a single source or a set of sources. It shows as a red icon. It looks alarming, but the most common cause is innocent: Turnitin has matched your paper to an earlier copy of itself. Here is how to tell which cause applies and what to do.
The usual causes of 100% (or 90%+) similarity
| Cause | How to spot it | What to do |
|---|---|---|
| Your own earlier submission | Top source is "Submitted to [your university]" with your submission date | Ask your instructor to exclude that source or have the earlier copy removed |
| A draft assignment stored your paper | Top source is a draft you submitted in the same course | As above; ask for drafts to be set to "no repository" next time |
| A group member submitted the same file | Top source dated the same day as your group's deadline | Tell your instructor it is a group submission |
| A checking site stored your paper | Top source is "Submitted to [another institution]" before your submission | Explain to your instructor and show your drafts |
| Your work is already published | Top source is a journal article or repository page by you | Normal for theses by publication; cite your own article |
| Copied work | Top source is someone else's paper or web page | Substantial rewriting with proper citation |
Why resubmitting causes 100%
Within one assignment, a resubmission replaces your earlier file, so it does not match itself. The problem happens across assignments. If you submitted to a draft assignment, a different course or a free checker that saves papers to the student repository, your final submission matches that stored copy word for word. See what happens when you resubmit.
Can an instructor remove the match?
Yes. Your instructor can exclude a source from the report, and the score is recalculated without it. Removing a paper from the repository permanently is a request your institution's Turnitin administrator makes to Turnitin. Give your instructor the source number and date shown in the report.
How to avoid it next time
- Ask whether draft assignments store papers before you use them.
- Do not run your final paper through checkers that add it to the student repository.
- For group work, agree who submits the file.
- Use a pre-check that does not store your paper. Ours runs without adding your document to the repository.
What a normal similarity report looks like
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.
See also: what each Turnitin percentage means and how to fix plagiarism flagged by Turnitin.
Frequently asked questions
Why is my Turnitin similarity 100%?
Most often because your paper matches an earlier copy of itself stored in the student repository, from a draft assignment, another course or a checking site.
Can my instructor remove the match to my own paper?
Yes. Your instructor can exclude the source, and your institution's Turnitin administrator can ask for the stored copy to be removed.
How do I avoid 100% similarity next time?
Avoid tools that store your paper in the repository, ask whether draft assignments store papers, and agree who submits group work.