Direct answer
Grammarly can flag text that looks AI-generated, but it is not a ChatGPT checker in the sense students usually mean: it does not produce the same AI score your university sees in Turnitin. Grammarly's AI detector returns a probabilistic percentage for pasted text, while Turnitin's AI writing report is a separate, confidence-thresholded indicator embedded in the similarity report your instructor opens [1][2]. Because the two tools use different models, different thresholds, and different text inputs, a clean Grammarly result does not guarantee a clean Turnitin result.
Does Grammarly Detect ChatGPT-Written Text Accurately?
Grammarly's AI detector is built to estimate whether a passage reads as machine-generated, and it does that reasonably well on long, unedited blocks of ChatGPT output. It returns a percentage alongside highlighted segments, so you can see which sentences triggered the flag rather than only an overall number [2]. That sentence-level view is genuinely useful for revision, because it tells you where the prose became formulaic.
Accuracy is the weaker part of the story. Grammarly describes its detector output as probabilistic and explicitly cautions against treating a result as proof that a person did or did not write the text [2]. Detection models respond to surface patterns — uniform sentence length, low burstiness, predictable transitions, generic hedging — and those patterns also appear in human writing that has been heavily polished or produced under time pressure.
There is a second accuracy problem specific to ChatGPT: the models change. A detector calibrated against one generation of output can drift when the underlying model's phrasing shifts, which is why detector vendors retrain continuously and why results for the same paragraph can move between versions [2]. Treat any single Grammarly verdict as one data point, not a ruling.
Finally, Grammarly only sees what you give it. If you paste a cleaned-up excerpt rather than the full document, or paste it after you have already rewritten the flagged sentences, the score describes the excerpt you pasted, not the file you will upload to your course portal.
Why Do Grammarly and Turnitin Give Different AI Scores for the Same Essay?
The two systems answer slightly different questions. Grammarly estimates how AI-like a piece of pasted text appears; Turnitin runs AI writing detection as a component of the similarity report, producing an overall percentage plus sentence-level highlighting inside the same report your instructor already uses for matching text [1]. Different training data, different confidence handling, and different segmentation mean the numbers are not interchangeable.
Turnitin's own documentation is candid that false positives occur, particularly with highly formulaic writing, non-native English phrasing, and text that has been heavily edited or paraphrased [3]. The score is presented as a signal to support academic judgement, not as standalone evidence of misconduct [3]. That framing matters for students: a high Turnitin percentage is a conversation starter for an instructor, not an automatic finding.
Practically, this is why students report a low Grammarly number and a high Turnitin number for the same file. The Grammarly check may have run on a pasted subset, or on a version before your last round of edits; Turnitin processed the actual submitted document, in the format your institution accepts, with its own thresholds [1][3]. Neither tool is "wrong" — they are measuring different things on different inputs.
The useful takeaway is directional rather than numeric. Use a general-purpose checker to find the sentences that read as machine-like and fix them; use a report that mirrors your institution's system when you need to know what your instructor will actually see.
How Can I Preview the Turnitin AI Score Before I Submit?
Previewing the institutional view means running your draft through a Turnitin-compatible check rather than a general writing assistant. Turnitin's guidance for students centres on confirming with your instructor which tools and draft workflows are permitted in your course, because institutional settings and repository rules vary by school [4]. A draft check that adds your file to a student paper database is materially different from a non-repository check, and that distinction should be settled before you upload anything [4].
Turnitin0 exists for exactly this step. You upload a .docx, .pdf, or .txt file (English, 300–30,000 words, under 20 MB) and receive two PDFs in one order: a Turnitin AI detection report and a similarity report, formatted the way instructors see them in their LMS. Files are checked without being added to Turnitin's student paper database, and you can delete them from your account afterwards. Turnaround is under 15 minutes in 98% of cases, with delivery guaranteed within 30 minutes even during queue spikes.
One detail worth knowing before you read any report: Turnitin shows *% instead of an exact figure when AI detection falls below its 20% confidence threshold. That asterisk is a low-confidence signal, not a hidden high score — a distinction that trips up a lot of students comparing screenshots.
If Grammarly told you your draft was fine and you still want to know what your instructor's Turnitin AI report will say, close the gap before the deadline rather than after it. Turnitin0 gives you the actual AI and similarity reports — the same view your professor opens — so you can fix flagged sentences while there is still time to revise.
※ Turnitin0.com - Actual Turnitin AI Report Cover, Score, Flag And Similarity Summary
FAQ
Is Grammarly a ChatGPT checker?
Only in a loose sense. Grammarly's AI detector estimates whether pasted text looks machine-generated and returns a percentage with highlighted segments [2], but it is not built to reproduce the AI writing indicator inside a Turnitin report [1].
Can Grammarly's AI score predict my Turnitin score?
No. The two tools use different models, thresholds, and inputs, and Turnitin explicitly notes that false positives occur and that its score should support rather than replace academic judgement [3]. Use Grammarly to locate formulaic sentences, not to forecast an institutional number.
Why does Turnitin show an asterisk instead of a percentage?
An asterisk appears when AI detection falls below Turnitin's 20% confidence threshold. It signals a low-confidence result rather than a concealed high score.
Does checking my draft with a third-party tool get me in trouble?
That depends on your institution. Turnitin advises students to confirm permitted tools and draft workflows with their instructor, since repository and submission rules vary by course [4]. A non-repository check does not add your file to the student paper database.
What should I do if my draft is flagged?
Revise the flagged passages in your own voice — vary sentence rhythm, replace generic transitions, and add specific evidence or examples. Then re-check the actual file you plan to submit, in the format your course accepts [1].