Direct answer
Grammarly does offer an AI detector, and it can be used without a paid subscription, but it is not a free Turnitin check — it returns a probability estimate from a general-purpose writing platform rather than the institutional report your university runs. Grammarly itself describes the output as a likelihood score and cautions that no detector is fully accurate, especially on short passages [1][2]. That distinction matters: a clean result on a free Grammarly check does not guarantee a clean result in Turnitin, because the two systems are trained on different data and report different things [3]. If your goal is to know what your professor will actually see, you need a report produced by the same detection engine your institution uses [4].
Does Grammarly Have a Free AI Detector, and How Accurate Is It?
Yes — Grammarly's AI detector exists and is accessible to free users as part of its writing platform, returning an estimated percentage of text it considers AI-generated alongside a human-written balance [1]. It is worth being precise about what that number means. Grammarly presents it as a probability, not a finding of misconduct, and its own documentation frames the tool as guidance for writers and educators rather than an adjudication instrument [1][2]. Accuracy is therefore conditional: it is a signal, not a verdict.
The reliability of that signal drops sharply with text length. Grammarly notes that shorter passages give less dependable output, and that results can shift as text is edited, because the detector is reading statistical patterns rather than tracing provenance [2]. A 150-word discussion post and a 4,000-word dissertation chapter are not comparable inputs, and neither is a paragraph you rewrote by hand after the first draft. Detectors also cannot distinguish "AI wrote this" from "this reads like the register AI tends to produce," which is why heavily formulaic academic prose sometimes trips them.
There is a second, more practical limitation for students. Grammarly's detector is built for general writing, not for the specific long-form English academic prose that institutional systems are tuned to evaluate [3]. That mismatch is the single biggest reason a free Grammarly result and a Turnitin result can point in opposite directions on the same document. Treat the free check as a rough early warning during drafting, and not as the number that decides whether you are safe to submit [2][3].
Why Do Free AI Detectors Disagree With Each Other and With Turnitin?
Different detectors answer different questions, so disagreement is expected rather than evidence that one of them is broken. Turnitin's AI writing indicator reports the percentage of qualifying text flagged as AI-generated, and it deliberately withholds precision when the overall score falls below its confidence threshold — displaying *% instead of an exact figure because the signal is weak at that level [3]. A free tool that always prints a hard number is not being more honest; it is being less careful about low-confidence output.
Turnitin also scopes its detection narrowly, focusing on long-form, English, academic-style prose, and it explicitly states that its score is not definitive proof of misconduct and should be read in context by an instructor [3]. That framing is important for students: the report is designed to start a conversation, not to end one. A free detector that markets itself as a definitive answer is overstating what any pattern-matching model can deliver on a document it has never seen before.
The practical consequence is that you should never average two detector scores or assume the higher one is "the truth." Compare like with like. If your institution runs Turnitin, the only result that predicts your actual submission outcome is a Turnitin AI report, because it is generated by the same engine and presented in the same format your instructor reads [3]. Anything else — Grammarly included — is a second opinion from a different instrument.
How Can I Check My Draft Against the Same Turnitin AI Report My Professor Sees?
The report your instructor opens is generated inside the institutional similarity workflow, and it keeps two numbers separate: the similarity score for matched sources and the AI writing indicator for flagged prose [4]. Instructors do not just see a headline percentage — they see flagged segments highlighted inside the document, which is why the context of a flagged passage matters as much as its length [4]. Reproducing that experience requires a check run through the same detection engine, on the same kind of file, at the same length.
This is the gap a free Grammarly check cannot close, and it is worth being honest about why. A pre-submission Turnitin check returns two downloadable PDFs from one order: the AI detection report and the similarity report, formatted as the professor sees them in the LMS [4][3]. You get the score band, the highlighted passages, and the match list — the same artefacts you would otherwise encounter for the first time after the deadline has passed.
Practical sequencing helps here. Draft normally, run a free detector early to catch obvious register problems, revise the flagged paragraphs yourself, and only then spend money on a Turnitin check once the text is close to final [2][4]. Checking a rough draft against an institutional engine wastes the check; checking a polished draft tells you something actionable. And if the report comes back with *% rather than a hard number, read that as a low-confidence signal rather than a pass or a fail [3].
If you have reached the point where a free estimate is no longer enough — where you need the actual report, with the actual score band and the actual highlighted passages — turnitin0 runs that check for you before your deadline does it for you. Upload a .docx, .pdf, or .txt file (English, 300–30,000 words, under 20 MB) and you get both the Turnitin AI detection report and the similarity report back, typically in under 15 minutes, without your file being added to Turnitin's student paper database.
※ Turnitin0.com - Actual Turnitin AI Report Cover, Score, Flag And Similarity Summary
FAQ
Is Grammarly's AI detector really free?
Grammarly's AI detector is available without a paid plan, but "free" here means access to a probability estimate rather than an institutional-grade report [1]. It is a useful early warning during drafting, not a substitute for the check your university runs.
Can a free AI detector get me accused of misconduct?
No detector score is itself a misconduct finding. Turnitin states plainly that its AI writing indicator is not definitive proof and should be interpreted in context by an instructor [3]. What causes trouble is submitting text you never verified, not the act of running a free check.
Why does Turnitin show *% instead of a percentage?
Turnitin displays *% when the overall AI score falls below its 20% confidence threshold, meaning the signal is too weak to report precisely [3]. It indicates low confidence, not a guaranteed clean result.
Does Grammarly check the same things as Turnitin?
Not the same things and not on the same basis. Grammarly's detector is a general writing tool, while Turnitin's detection is scoped to long-form English academic prose and delivered alongside a separate similarity report [2][4]. Two different instruments will sometimes disagree.
What file types and length can I check before submitting?
A pre-submission Turnitin check accepts .docx, .pdf, or .txt in English, with a word count above 300 and below 30,000, and a file size under 20 MB. You receive the AI detection report and the similarity report together, and the file is not added to Turnitin's student paper database [4].