If your university uses Turnitin, your essay gets checked against a database of billions of web pages, journals, and previously submitted student papers before your tutor even opens it. Here's what it actually looks at, what counts against you, and how to see your score before you submit.
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The similarity score compares your text against Turnitin's database and flags matching or near-matching passages — this is the plagiarism-style check most students already know about.
Separately, Turnitin also runs an AI writing indicator, which estimates how much of the text shows patterns associated with AI generation. This is a different number, checking for a different thing, and it's the one that trips people up because a high similarity score and a high AI score mean two completely different problems.
Quoted material, properly cited references, and your bibliography all get picked up and counted — that's normal and expected. Most UK universities look at the report manually rather than applying a hard cutoff, because a 25% score made up of correctly cited quotes is very different from a 25% score made up of uncited copied paragraphs.
What tutors actually look for is unattributed matching text — long unbroken passages that match another source with no quotation marks or citation.
Turnitin itself has acknowledged that AI detection isn't perfect — it works by pattern-matching against how AI models tend to write (very even sentence rhythm, generic phrasing, low 'burstiness'), which means heavily edited human writing can occasionally score higher than expected, and lightly-edited AI text can sometimes score lower.
Because of that, it's worth checking your own writing before you submit, especially if you tend to write in a very structured or formal style, which can occasionally read as more 'AI-like' to these systems.
See how your writing scores against multiple AI detection methods before your tutor does — free, no account needed for your first check.
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