This question has an unusual paper trail: it was asked directly, by name, on Turnitin's own official community forum — and a Turnitin staff member responded without actually answering it. Here's what was said, why the honest answer is "it depends which Grammarly feature you used," and what that means for a draft you're about to submit.
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On Turnitin's official community forum, a thread titled "AI Detection and Grammarly" has a user, Eileen Lee, asking directly whether Turnitin's AI detection can distinguish grammar correction or paraphrasing from AI-generated ideas and content. A Turnitin Customer Engagement Specialist, Gill Rowell, replies in the thread — but doesn't give a yes-or-no answer to that specific question. Her response instead points out that Grammarly comes in different versions, and that one of those versions "offers generative AI," which means a claim of "I just used Grammarly" needs to be checked against which specific features were actually used before it means anything.
Separately in the same thread, Steve Bentley — a university administrator for Turnitin at his institution, not a Turnitin employee — says he's heard "unsubstantiated reports" of Grammarly and Quillbot output getting misdetected, without specifying which versions or features were involved. And one user in the thread, posting as Ammar202, reports a concrete case: their own human-written text, after being rephrased with Quillbot, was flagged as AI-generated. That's a single anecdote, not a controlled test, but it's a documented case of a paraphrasing tool producing a false positive on genuinely human writing — which is the closest thing to real evidence in a thread that otherwise has no official answer.
"Grammarly" isn't one single feature, and that's the whole crux of why Turnitin's own staff response hedged. Basic spelling and grammar corrections are a different thing, mechanically, from Grammarly's generative features — full-sentence rewrites, tone adjustment, and (on some plans) AI-assisted drafting. The former touches individual words; the latter can replace entire sentences with newly generated phrasing, which is structurally closer to what AI-detection tools are actually built to notice.
Grammarly itself ships a feature that exists specifically because this ambiguity is real: Authorship. It's an opt-in tool that tracks your writing process in Google Docs, Microsoft Word, or the Grammarly Editor, and produces a shareable report color-coding each sentence by where it came from — typed by you, pasted from elsewhere, or suggested by Grammarly. If you've used Grammarly's AI features and want to be able to show exactly which sentences came from where, that's the documented way to do it — not something a generic AI detector is built to tell you after the fact.
The honest summary of all of the above: there's no published Turnitin statement guaranteeing Grammarly use is safe, and no published statement confirming it's reliably flagged either — the question is genuinely unresolved in public, even on Turnitin's own forum. What's more consistent across the available evidence is that heavier use of generative rewriting (full-sentence rewrites especially) tends to introduce the kind of uniform, pattern-heavy phrasing that general AI detectors are built to catch, regardless of which tool produced it. Light, mechanical corrections are a different risk profile than letting a tool regenerate whole sentences.
Turnitin is explicit in its own materials that an AI-writing flag is meant to be one input for a human reviewer's decision, not an automatic verdict — which is the same standard worth applying here. Checking your draft against a detector before you submit, the way you'd check any other AI-assistance question, at least tells you what a report might flag before it's the one your instructor sees.
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