Does Turnitin detect copy and paste?
Yes, and that is the similarity check, which works completely differently from the AI indicator sitting next to it. Confusing the two is the most common mistake made about these reports.
Copy and paste is exactly what a similarity checker was built to find. It matches your text against a database of web pages, publications and previously submitted work, and reports the overlap with a link to where it came from.
That is a lookup. It finds something and shows you the something.
The other score works nothing like it
The AI indicator on the same report matches nothing. It is a classifier's probability that your writing has the statistical properties of generated text: predictable word choice, and sentence lengths that stay close to each other.
Nothing was found, so there is no source to click through to and nothing to check. It comes with an error rate instead of a citation.
The two sit side by side in the same visual style, which is why people read them as the same kind of evidence. They are not. See how Turnitin AI detection works.
The consequence that catches people out
Generated text is original. A model does not copy from a source, it produces new wording. So generated text usually returns a low similarity score.
A clean similarity report therefore says nothing at all about what the AI indicator reported. The two are independent, and a document can be clean on one and high on the other in either direction.
Whether pasting matters for the AI score
Not directly. The indicator reads the finished words, so it has no way to know how they arrived in the document. Pasting your own writing in from another file changes nothing about the text.
What does change the score is what the text is like:
Even sentence rhythm, the strongest signal. Human academic writing in our corpus varies sentence length with a standard deviation of 8.7 words, generated text with 6.4.
Formal, conventional phrasing, which is predictable by construction.
Heavy editing, because smoothing removes variation.
See why AI detectors flag human writing.
One reason to draft in a document rather than paste at the end
Not because pasting is detected, but because of what it costs you in record.
A document written in Google Docs or Word with autosave keeps version history showing the text growing over hours. A document that appears in a single paste has none of that. If a question ever arises, version history is the strongest thing you can point at. See how to show you wrote your essay.
How often the AI indicator is wrong
Turnitin publishes it: 4% of genuine human writing. Ours is 0.4%, which is 99.6% specificity, measured on 15,900 documents of real academic writing.
Since you cannot see either score before submitting, the only check available is one you run yourself.
Ours is free and unlimited with no account, takes .pdf, .docx and .tex, has no word cap, scores every paragraph separately, and never stores your text.