3 October 2026 · 8 min read
Here is a situation we see every submission season. A student wants to know their similarity score before handing in a thesis, so they ask a friend at another college, a teacher, or a cyber café with “Turnitin access” to run it. The score looks fine. Weeks later they submit through the department and the report comes back at 90% or more — matched almost entirely to a single source. The source is their own earlier upload. This post explains why it happens, how to avoid it, what to do if it already has, and where reusing your own work genuinely does cross a line.
Turnitin keeps a repository of submitted student papers. When an assignment is set up to store submissions, every file uploaded through it is added to that repository, and every later document is compared against it. That is what lets the system catch a thesis copied from last year's batch.
It also means that if your thesis was uploaded through someone else's class or account with storage switched on, your own text now sits in the repository as a separate submission. When the department later checks your final version, Turnitin finds a near-perfect match — to you. The report does not know the two files have the same author. It shows a single source covering most of the document, which at a glance looks like the worst possible case of copying.
The same thing happens on a smaller scale with a proposal or a chapter checked early on a borrowed account. Every stored upload is something your final submission can collide with.
Group work creates a version of it too. If one member of a group uploads a shared draft somewhere that stores it, every other member's later submission can match that copy, and the report will list it as another student's paper.
A pre-submission check is worth having. It just needs to be run in a way that does not leave a copy behind.
Do not panic and do not start rewriting. Rewriting a thesis to get away from a match against your own earlier upload damages your work to solve a problem that is administrative, not academic.
Open the report and confirm what is going on. If the dominant source is listed as a student paper submitted to another institution or class, around the date you had the pre-check done, that is almost certainly your own upload. Note the date and the source details shown.
Then talk to your supervisor or the person handling submissions, early and plainly. Explain that you had the document checked beforehand and the earlier copy appears to have been stored. Whoever administers the institution's account can usually exclude that source from the report, so the rest of the document is judged on its own; removal of a stored paper from the repository is generally something only the account that holds it can request. Procedures differ between institutions, so ask what yours does rather than assuming.
Bring evidence: your drafts, version history, and the date and place of the earlier check. A supervisor who has seen your work develop over months is usually quick to recognise what has happened. Raising it yourself, before anyone asks, puts you in a far better position than waiting for it to be noticed.
The repository trap is an accident. Self-plagiarism is a different question: reusing your own previously submitted work as if it were new. Whether it is a problem depends entirely on context.
Reusing your proposal in your thesis is usually expected. Your introduction, objectives and methodology chapters grow directly out of the approved proposal, and supervisors know this. It will often match on a check if the proposal was stored. That is normal, but it is worth expanding and updating the text rather than pasting it unchanged — a proposal is written in the future tense about work you planned, and the thesis reports work you did. If you are unsure whether your department expects you to flag the overlap, ask your supervisor.
Reusing last semester's assignment for a new module is a different matter. Submitting the same work for credit twice without permission is treated as academic misconduct at most institutions, even though every word is yours. If an earlier piece is genuinely relevant, ask the module leader first, and cite your earlier work as you would any other source.
Publishing from a thesis is a third case. Turning a chapter into a journal article is normal academic practice, but journals expect you to disclose that the work comes from your thesis, and many run their own similarity checks. Disclosure answers the question before it is asked.
Related reading:
Worried a check you already had done has left a copy behind, or not sure what your report is showing? Send the document on WhatsApp. We run pre-submission checks without storing your file, and return a plagiarism report and an AI writing report with every match explained.
Tell us what you need checked and when it is due. Your document is checked without being stored in any student-paper repository, so the check never counts against your real submission. The reports come back with what each match means, not just a percentage.