Is Grammarly's AI Detector Accurate? How to Read It (2026)

Grammarly's AI detector is a useful first check, not a verdict. It reads your text in sections and returns an estimated percentage that "appears to be AI-generated." Grammarly claims 99% detection accuracy, but that is its own figure, and the company also says no detector is 100% accurate and a result shouldn't be the only evidence. So a score can be wrong in both directions: human writing can be flagged, and lightly edited AI text can pass.

What does Grammarly's AI detector actually show?

Based on Grammarly's AI detector page (checked October 2026), you paste text or upload a file and get a line like "X% of this text appears to be AI-generated." The result splits into two buckets: "Resembles AI text" and "No AI text patterns found."

Grammarly says it splits the text into sections, looks for language patterns it associates with AI writing in each one, and returns an estimate. The basic scan is free with an account. A paid Pro plan adds an AI Detector agent that points to the parts that may read as AI-generated and helps you rework them.

Two things worth keeping straight:

• The detector and Authorship are different. The detector guesses from how the text reads. Grammarly's Authorship feature records how a document was written, such as typed or pasted. Grammarly says Authorship "may not capture 100% of cases accurately," for instance when text is typed very fast or pasted from a desktop source it can't see.
• A percentage isn't a share of authorship. "30% AI" means 30% of the text matched patterns the model links to AI. It doesn't mean a third of the words came from a chatbot.

How accurate is it, really?

Here is what is on record, as of October 2026:

That last row matters. When you see a confident "Grammarly's false positive rate is X%" on a review site, check who wrote it and how they tested. Vendor claims and affiliate reviews both have reasons to push a number.

The wider research is clearer than any single product test. A well-known 2023 study by Liang and colleagues, GPT detectors are biased against non-native English writers, found several detectors wrongly flagged a large share of essays by non-native English speakers. It tested other detectors, not Grammarly's, but the lesson carries: simple, formal or formulaic English can look "AI-like" to a classifier.

When is a Grammarly flag most likely to be wrong?

These are the situations where a score deserves extra doubt. They come from how classifiers work in general and from Grammarly's own caveats, not from a test of Grammarly's model:

1. Short text. Fewer words give the model less to go on.
2. Formal or templated writing. Cover letters, lab reports, policy documents and legal-style prose are predictable by nature.
3. Non-native English. Careful, plain phrasing and common word choices can read as machine-like.
4. Text you ran through Grammarly's own suggestions. Heavy smoothing makes writing more uniform. Uniform writing is easier for a classifier to read as machine-like.
5. Light edits to AI text. This is the reverse risk: the detector can pass a draft that is mostly AI because a few sentences were changed.

What to do when it flags your own writing

Use this as a checklist before you argue with a number:

1. Don't rewrite to chase a score. Changing words until a percentage drops proves nothing, and it can make the writing worse.
2. Save your process. Version history in Google Docs or Word, earlier drafts, notes, outlines and research links. Dates matter.
3. Read the flagged passages. Is it the formulaic intro, the definitions, the transitions? That tells you what a reader might also find generic.
4. Get a second opinion. Run the same text through another detector. If they disagree sharply, that's evidence the signal is weak. Our post on why GPTZero and ZeroGPT disagree explains how.
5. Explain your process calmly. Here is a template you can adapt:

Hi [Name], I saw that [tool] reported part of my [essay/report] as AI-generated. I wrote it myself, and I can share my drafts, version history and notes from [dates]. Detector scores are estimates and can flag human writing, so I'd like to walk you through how I wrote it. When would suit you?

If the person asking is a teacher, the first question is also whether you know which detector your school uses, because Grammarly's result is not what an instructor will necessarily see.

Is Grammarly's detector the same as Turnitin's?

Grammarly presents its detector as its own tool, and nothing in its documentation says it shares a model with Turnitin. Two different classifiers can disagree on the same text, so a clean Grammarly result doesn't predict a Turnitin result, and a flag doesn't either. Use each result for what it is: one tool's estimate.

Checking your own draft with Unflag

If you want a second opinion on your own writing, Unflag's AI Detector shows an overall AI score, an AI-generated vs human-generated split and a verdict of Likely AI-generated or Likely Human-written (above 50% reads as AI). It works on the web and in the iPhone and Android apps. Free accounts can check up to 600 characters per input a few times a day, and the text needs to be at least 50 words. Plus raises the limit to 10,000 characters. As of October 2026, Plus is $8.99 a month or $45.99 a year on the web, and $6.99 a week in the apps.

Keep the limits in mind. Unflag's detector is its own model, so its score can't predict what Grammarly, Turnitin or any other tool will say. Results are saved to your History. It's a way to see how your draft reads, not a judge of anyone's honesty.

If the draft reads stiff, you can edit it yourself using the signs of AI writing checklist, or use Unflag's Rewrite tool to improve the writing while keeping your meaning. Either way, the goal is clearer writing in your own voice, not a lower number. For how a newer detector explains its labels, see how the Pangram AI detector works. If you're choosing a tool that pairs a rewriter with a detector, our QuillBot alternatives roundup compares options.

Honest caveats

• We compared Grammarly's published pages, October 2026. We did not run our own accuracy test, so we give no false positive rate for Grammarly or anyone else.
• Grammarly updates its product often. Re-check its pages before relying on a feature or limit.
• Any detector, Unflag's included, is a signal about text patterns. It can't show who wrote something or whether AI use was allowed. Follow your school's or employer's policy, and say so when you used AI where disclosure is expected.

Bottom line

Read Grammarly's percentage as a prompt to look closer, not as a finding. If it flags your own work, keep your drafts, get a second opinion and explain your process. If you want to check a draft yourself before you send it, Unflag's AI Detector is a free-to-start option on the web and your phone.

Frequently asked questions

Is Grammarly's AI detector accurate?

Grammarly says its detector reaches 99% detection accuracy and ranks first on the RAID benchmark, but those are its own claims. The same page admits no AI detector is 100% accurate and says a result shouldn't be used as a standalone verification method. Treat the percentage as an estimate, not a verdict.

Can Grammarly's AI detector give a false positive?

Yes. Grammarly itself says AI detectors can get it wrong, and that human writing can be flagged while lightly edited AI text can pass. Formal, formulaic or non-native English writing is the usual risk, so keep drafts and version history for anything that matters.

Does Grammarly's AI detector use Turnitin?

Grammarly presents its AI detector as its own tool, and nothing in its documentation says it shares a model with Turnitin. They can disagree on the same text, so a low Grammarly score doesn't predict what a school's detector will show, and the reverse is also true.

What does a Grammarly AI score of 30% mean?

It means Grammarly estimates that about 30% of the text has patterns it associates with AI writing, with the rest showing no AI patterns. It does not say a third of your text was written by AI, or that you did anything wrong. Read the flagged passages, not just the number.

What should I do if Grammarly says my own writing is AI?

Don't rewrite in a panic. Save your drafts, notes and version history, run the same text through a second detector, then explain your process calmly to whoever is asking. A single score is weak evidence, and a documented writing process is much stronger.

Is there another way to check my own draft for AI patterns?

Yes. Unflag's AI Detector gives an overall AI score, an AI-generated vs human-generated split and a Likely AI-generated or Likely Human-written verdict. It is a different model from Grammarly's, so use it as a second opinion on your own draft, not as a prediction of anyone else's result.