Does Turnitin detect AI?
Yes, on almost every submission, automatically, and you never see the result. Those three facts matter more than the first one.
Turnitin runs an AI indicator alongside its similarity check. It runs by default in most institutional configurations, it runs on submission, and the report it produces is visible to staff rather than to you.
So the question people mean when they ask this is usually the next one: what does it detect, how often is it wrong, and what can be done about it.
What it detects, and what it does not
It detects regularity. Predictable word choice, and sentence lengths that stay close to each other. Generated text has both, because a model samples likely continuations and produces an even rhythm.
It does not detect use. There is no record in the words of how they were produced, no watermark and no lookup. The indicator is a classifier's probability, which is why it comes with an error rate rather than a source you can open.
That is the difference between it and the similarity score sitting next to it on the same report. Similarity matches your text against a database and shows you where. The AI indicator matches nothing. See how Turnitin AI detection works.
How often it is wrong
Turnitin publishes the figure: 4% of genuine human writing gets flagged.
Ours is 0.4%, which is 99.6% specificity, measured across 15,900 documents of real academic writing.
Two further numbers Turnitin publishes are worth carrying:
Below 20% is less reliable. Documents scoring under 20% show a higher incidence of wrong flags, because a low percentage is built from a small flagged region.
Wrong flags cluster. Their analysis found 54% of falsely flagged sentences sit directly beside a genuinely flagged one and 26% two sentences away. Four in five land next to a real detection, so a flagged region is wider than whatever caused it.
What it detects most readily in human writing
The writing that scores high is the writing that is regular for ordinary reasons.
Formal, conventional prose, which is what you are asked to produce.
Methods, procedures and literature reviews, formulaic by design.
Heavily revised work. Every editing pass smooths, and smoothing removes variation. Our corpus puts human academic writing at a within-document sentence-length standard deviation of 8.7 words and generated text at 6.4.
Writing in English as a second language, repeatedly measured at elevated rates in published evaluations. See why non-native English writing gets flagged.
Does it detect specific tools
Not by name. It reads properties of the text, so what matters is what a tool does to those properties rather than which company made it.
Paraphrasers change vocabulary and leave sentence structure intact, which is where most of the signal lives. See does QuillBot get flagged.
Editing assistants smooth prose, which raises the score rather than lowering it. See does Grammarly get flagged as AI.
Copy and paste is a similarity question, not an AI one, and the two behave completely differently. See does Turnitin detect copy and paste.
The only part you control
You cannot run Turnitin yourself. It is licensed to institutions and there is no student version. See can I use the Turnitin AI detector myself.
What you can do is score the document before you submit it, per paragraph, and fix the passages that read flat. The changes are mechanical and leave your argument alone: vary sentence length, cut connective openings, put the specific detail back. See check your essay before you submit it.
Ours is free and unlimited with no account, takes .pdf, .docx and .tex, has no word cap, and never stores your text.