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Will Grammarly get flagged as AI?

Grammarly is one of the most common writing tools students use, so this question comes up constantly. The short version: spelling and grammar fixes are generally fine, and letting Grammarly write or rewrite your text is where the risk is. Here's the detail.

Updated October 10, 2026 · By the IsThisAI? team

Grammar fixes vs. generative AI

Grammarly does two very different jobs, and AI detectors treat them differently.

• Correcting your writing. Spelling, grammar, punctuation, and small word-choice suggestions. You wrote the sentence; Grammarly tidied it.
• Generating writing. Grammarly's generative AI features can draft text from a prompt, paraphrase or rewrite paragraphs, summarize, and change tone. In that case the tool composed the words.

Turnitin, the detector most schools use, draws the line in the same place. Its FAQ says the detector "is not tuned to target Grammarly-generated spelling, grammar, and punctuation modifications," and that in its tests on human-written documents, "in most cases, changes made by Grammarly (free & premium) and/or other grammar-checking tools were not flagged as AI-written." In the same answer it says this "excludes content generated by Grammarly's generative AI-powered features, including draft generation, paraphrasing, summarizing, and other features," and that such content "will likely be flagged as AI-generated" (Turnitin FAQ).

Notice the hedge: "in most cases." Grammar fixes aren't a guaranteed pass, they're just not what the detector is looking for.

Why a grammar-checked essay can still get flagged

Turnitin says its false positives tend to involve "content without a lot of structural variation, text that literally repeats itself, or text that has been paraphrased without developing new ideas" (Turnitin FAQ). If you accept dozens of "clarity" suggestions that make every sentence a similar length and shape, the result can drift toward that smooth, uniform style. That's our reading of how it could happen, not something Turnitin has measured.

Some writers are also flagged more often no matter what tool they use. Detectors have been shown to flag essays by non-native English writers far more often than essays by native speakers, largely because of simpler, more predictable word choices (Liang et al., 2023). If that's you, keeping drafts matters even more.

Try it yourself

The easiest way to see the difference is to test it on your own writing with our free detector:

1. Paste a few paragraphs you wrote without help and check the score.
2. Run the same text through Grammarly, accept only spelling and grammar fixes, and check again.
3. Now ask an AI tool to "rewrite this to sound more professional" and check that version.

Our detector isn't Turnitin and results won't match exactly, since every detector is a different model. But seeing which version reads as more AI-like is a quick way to learn where your own line is. Remember that no detector is fully reliable; see are AI detectors accurate? for why.

Safe ways to use Grammarly on school work

1. Check your course policy first. Some instructors allow grammar checkers and ban generative AI; some ban both. When in doubt, ask, and get the answer in writing.
2. Stick to corrections. Accept spelling, grammar, and punctuation fixes. Be choosier with suggestions that rewrite whole sentences.
3. Skip the generate, rewrite, and paraphrase buttons for graded writing unless your instructor explicitly allows them. That's the part Turnitin says will likely be flagged.
4. Keep your voice. If a suggestion makes a sentence sound less like you, ignore it. Varied, slightly imperfect writing is normal human writing.
5. Keep a record. Write in Google Docs or cloud-saved Word so version history builds as you go. Grammarly's Authorship feature can also track a document and create a shareable report that separates what you typed from what was pasted or AI-generated (Grammarly Support). It only works if you switch it on while writing.

If you're ever questioned, that record is worth far more than any detector score. Our guide on how to prove you didn't use AI explains how to use it.

What about other grammar checkers?

Turnitin's statement covers "Grammarly (free & premium) and/or other grammar-checking tools," so the same logic applies to tools like Microsoft Editor or the spell check built into Google Docs (Turnitin FAQ). And the same exception applies too: any feature that writes or rewrites text for you is on the generative side, whatever it's called. Turnitin also says it looks for text changed by AI paraphrasers and word spinners (Turnitin Guides). For more on how Turnitin handles specific tools, see Can Turnitin detect ChatGPT, Claude, and Grammarly?

More guides

Sources

1. Turnitin, "Turnitin's AI writing detection capabilities FAQs" (Turnitin Guides, updated Oct 7, 2026). https://www.turnitin.com/products/features/ai-writing-detection/faq
2. Grammarly Support, "Introducing Authorship". https://support.grammarly.com/hc/en-us/articles/29548735595405-Introducing-Authorship
3. Liang, Yuksekgonul, Mao, Wu & Zou, "GPT detectors are biased against non-native English writers," Patterns 4(7), 2023. https://www.cell.com/patterns/fulltext/S2666-3899(23)00130-7
4. Turnitin, "Using the AI Writing Report" (Turnitin Guides). https://guides.turnitin.com/hc/en-us/articles/22774058814093-Using-the-AI-Writing-Report

This guide is general information, not legal or academic-policy advice. AI detection results, including ours, can be wrong.