Does Turnitin Detect Grammarly? Grammar Fixes vs AI Rewrites

For ordinary spelling, grammar and punctuation fixes, Turnitin says no. It states that its detector isn't tuned to target those Grammarly changes, and that in its tests on human-written documents, edits from Grammarly's free and premium versions "in most cases" were not flagged as AI.

Text produced by Grammarly's generative AI features is a different story. Turnitin says content from drafting, paraphrasing, summarizing and similar features "will likely be flagged as AI-generated." Grammarly's own AI detector and its Authorship tool are separate products again: they don't change your text, and Turnitin's FAQ doesn't mention them.

So the useful question isn't "did I use Grammarly?" It's which part of Grammarly you used, and whether you can show it.

What Turnitin says, word for word

Turnitin answers the question directly in its AI writing detection FAQ, under "If students use Grammarly for grammar checks, does Turnitin detect it and flag it as AI?":

No. Our detector is not tuned to target Grammarly-generated spelling, grammar, and punctuation modifications to content but rather, other AI content written by LLMs such as GPT-3.5. Based on tests we conducted on human-written documents with no AI-generated content in them, in most cases, changes made by Grammarly (free & premium) and/or other grammar-checking tools were not flagged as AI-written by our detector. Please note that this excludes content generated by Grammarly's generative AI-powered features, including draft generation, paraphrasing, summarizing, and other features. Content produced using these features will likely be flagged as AI-generated by our detector.

Three phrases carry the weight:

• "In most cases." That isn't "never." Turnitin doesn't publish how often grammar-checked human writing was flagged in those tests.
• "Human-written documents with no AI-generated content." The reassurance covers your own writing plus corrections. It doesn't cover AI text that Grammarly then polished.
• "Excludes content generated by Grammarly's generative AI-powered features." Once Grammarly writes or rewrites the substance, Turnitin treats it like any other AI output.

Turnitin said much the same in 2024. Speaking to EdSurge, its chief product officer said that in the company's internal tests, traditional grammar-checking tools did not set off its detector.

"Grammarly" is really three different things

Most confusion comes from treating Grammarly as one tool. By Grammarly's own descriptions, it's at least three.

1. Writing suggestions

Grammarly describes these as its "foundational AI technology," which improves writing "through suggestions for spelling, grammar, clarity, conciseness, and tone." It says this technology "does not change the substance of the writing, and it cannot be turned off separately from Grammarly product offerings" (Grammarly Support).

One grey area: Grammarly's paid plan, now called Pro, adds "tone suggestions and full-sentence rewrites" (Grammarly plans; in some countries Grammarly also sells a Plus plan with the same writing features). Turnitin's reassurance names "spelling, grammar, and punctuation modifications." A suggestion that rewrites a whole sentence sits closer to the rewriting Turnitin excludes than a comma fix does. That's our reading, not a documented Turnitin threshold.

2. Generative AI features, including the humanizer

Grammarly says it introduced "optional generative AI features" in 2023 that "produce new content based on their inputs or prompts." These features "are not turned on by default," "can generate content and meaningfully change writing," and any user can switch them off in the Feature customization tab of their account settings.

Grammarly's generative AI guide lists on-demand help to "compose, rewrite, ideate, and reply," reached through a pencil or lightbulb icon. It also covers AI Chat, and Superhuman Go, an assistant that can draft content. Leeds Beckett University's library tells students these features are labelled "rewrite with Grammarly" and "Improve it" (Leeds Beckett).

Grammarly also offers an AI humanizer, which works in six languages. Its own FAQ is blunt: "This tool is not intended to bypass AI detectors. Instead, it enhances clarity and coherence" (Grammarly AI Humanizer). Turnitin says it looks for AI text "modified by AI paraphraser or bypasser (also called humanizers) tools," in English submissions. Our QuillBot and Turnitin guide explains how that paraphrase check works.

3. Grammarly's AI Detector and Authorship

Grammarly's AI Detector is free: paste text and get a percentage. Grammarly Pro adds an "AI Detector agent, which goes beyond a score." That score comes from Grammarly's model, not Turnitin's, so it isn't a preview of your Turnitin result. Grammarly itself says "there is no AI detector that can conclusively or definitively determine whether AI was used to produce text." We cover that detector's claims in does Grammarly detect AI writing?.

Grammarly Authorship is the more useful tool here. It's available on Grammarly Free and Pro and works in Google Docs, Microsoft Word and the Grammarly Editor. Grammarly says it can also be enabled on Canvas LMS submissions. It records whether each sentence was typed by you, pasted from a website, taken from a Grammarly suggestion, or AI-generated. You can replay the document's creation and share a color-coded report. It's opt-in, and "Grammarly doesn't auto-send it to your professor."

Watch the name clash. Turnitin also has a feature called Authorship, and it's unrelated. Turnitin says its Authorship "uses metadata as well as forensic language analysis to detect if the submitted assignment was written by someone other than the student," and "will not be able to indicate if it was AI written."

Why grammar-only users still get worried

The best-known case shows why this question keeps coming up. In 2024, EdSurge reported on Marley Stevens, a University of North Georgia student. She said a professor gave her a zero after Turnitin flagged a paper that she wrote herself, apart from standard Grammarly grammar and spelling checks. She also said the university placed her on academic probation.

EdSurge also reported that the university emailed students a warning: "One of the most commonly used generative AI websites being flagged by Turnitin.com is Grammarly." Turnitin, meanwhile, said grammar checkers didn't trigger its detector in its internal tests.

Both statements can be true, because "Grammarly" covers both grammar fixes and generative rewriting. Turnitin also lists its own causes of false positives: "content without a lot of structural variation, text that literally repeats itself, or text that has been paraphrased without developing new ideas." A detector can misfire on careful human writing with no Grammarly involved at all.

Turnitin's product chief gave practical advice in the same article: "make sure you could show teachers the evolution of your assignments or be able to answer questions." That's the standard to plan for.

How to document legitimate Grammarly use

1. Read your course's AI rule first. Some schools treat Grammarly's generative features as AI use that must be acknowledged. Leeds Beckett requires this "even if you are using the software to support a disability or language need."
2. If generative AI isn't allowed, switch it off. In Grammarly, go to Account, then Settings, then Feature customization, and toggle the generative AI features off. Your grammar and spelling suggestions keep working.
3. Turn on Authorship before you start writing. It only tracks from the moment you enable it, and the report can show which sentences came from you and which from a Grammarly suggestion.
4. Keep your version history. In Google Docs, anyone with edit access can browse earlier versions, and you can create named versions at milestones. File owners can also permanently delete version history (Google Docs help), so don't.
5. Write a one-line disclosure if your course asks for one. For example: "I used Grammarly for spelling and grammar suggestions only; I did not use its generative AI features." If you did use a generative feature, name it and say what it did.
6. If you're flagged, ask to see the report. The AI indicator is visible only to instructors, but they can download it as a PDF and share it with you (more on what students can see). Bring your Authorship report and version history, and point out that Turnitin says its percentage "should not be used as the sole basis for action." Our guide to proving your writing is your own covers the rest.

For a rough pre-check before you submit, SupWriter's AI detector gives one model's score with sentence highlights. It isn't Turnitin, and results vary by detector, text length and topic.

FAQ

Will free Grammarly get my essay flagged by Turnitin? Turnitin says spelling, grammar and punctuation changes from Grammarly's free and premium versions were, in most cases, not flagged as AI-written in its tests on human-written documents. It doesn't claim this holds in every case.

Will Grammarly's "Improve it" or rewrite features get flagged? Turnitin says content produced by Grammarly's generative AI features, including draft generation, paraphrasing and summarizing, "will likely be flagged as AI-generated by our detector."

Does Grammarly's AI humanizer get past Turnitin? Grammarly says its humanizer "is not intended to bypass AI detectors." Turnitin says it looks for AI-generated text modified by paraphrasers and humanizers in English submissions.

Can Turnitin see my Grammarly Authorship report? No, not unless you share it. Grammarly says the report isn't sent to anyone automatically, and your school can't see it unless you create a shareable link and send it. Turnitin's own "Authorship" feature is a separate product.

Is Grammarly's AI detector the same as Turnitin's? No. They're different models from different companies, so a Grammarly score isn't a preview of a Turnitin result. Grammarly's own detector page also warns that no tool can give a definitive answer about AI use.

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