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Turnitin AI Detection: What a *% Score Really Means

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Turnitin AI detection shows *% instead of a number when your AI score lands between 1% and 19%, and that asterisk is not a hidden "a little AI" verdict. Turnitin's own help center says it hides those numbers and highlights to avoid false positives, and its instructor guide calls results below 20% less reliable.

We follow the asterisk from Turnitin's May 2023 update to the July 2024 change that hid the numbers, look at where its false flags land (by Turnitin's 2023 figures, about 4 in 100 highlighted sentences may be human-written, 54% of them right next to real AI writing), what its under-1% false positive claim actually covers, and why Vanderbilt and Curtin switched the detector off. Then the practical part: Turnitin says the misconduct call is your teacher's, not the software's, so if you're questioned, ask to see the AI report and bring your drafts and notes.

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Cheat sheet

The short answer

Turnitin's AI detector estimates what percentage of a document's prose was likely written by AI, and highlights the sentences it predicts are AI-written. It is a prediction, not proof: Turnitin says its false positive rate is not zero and the score should not be the sole basis for action.

What the detector actually measures

  • The score is a percentage of qualifying prose sentences, not necessarily of the whole submission.
  • A file needs at least 300 words of long-form prose to get an AI score. Turnitin says the detector is meant for prose, not poetry, scripts, code, bullet points or tables.
  • From 1% to 19%, the report shows no number or highlights, only an asterisk (*%). Reports from before the July 2024 change may still show a number. Turnitin's guide says results below 20% are less reliable.

Claims versus evidence

ClaimWhat the evidence says
*% means no AI was foundNo. Something was flagged, between 1% and 19%. 0% is a separate result.
*% proves a little AI useNot proof. Turnitin hides the number to avoid false positives.
False positives are under 1%Turnitin states that only for documents with over 20% AI writing: about 1 in 100 fully human-written documents.
Every highlighted sentence is AIBy Turnitin's 2023 figures, about 4 in 100 highlighted sentences may be human-written.

What it cannot tell

Turnitin's 2023 figures show where wrong flags cluster. The model has been updated since.

  • Next to AI text. 54% of falsely flagged sentences sat right beside actual AI writing. Turnitin says an October 2026 update for English submissions targets these transition points; older reports are not rescored unless resubmitted.
  • Introductions and conclusions. More false positives appeared in the first and last few sentences.
  • Certain human writing. Turnitin's current FAQ says false positives can include text with little structural variation, repetitive text, and paraphrase that develops no new ideas.

Vanderbilt disabled the detector in August 2023, estimating that a 1% false positive rate could have wrongly labeled about 750 of its 75,000 papers from 2022. Curtin said it would disable it from 1 January 2026.

If your work is flagged

Turnitin's guidance says:

  • Turnitin makes no determination of misconduct; the final decision rests with the instructor.
  • The score is a single data point, not a definitive answer in isolation.
  • Students do not see the AI report by default. Instructors can share it as a PDF or make it available.

Sources: Turnitin help center, Turnitin FAQ, Turnitin guide, Turnitin update, May 2023, Vanderbilt, Curtin.

This cheat sheet as plain Markdown

In this video

  1. Why your Turnitin score shows *%
  2. What *% means: 1% to 19% AI
  3. How the asterisk changed: 2023 vs 2024
  4. Where false positives land
  5. The under-1% false positive claim
  6. Universities that switched it off
  7. Can your teacher still say you used AI?

Why your Turnitin score shows *% 0:00

Your Turnitin AI score shows just an asterisk? Should you worry? It's easy to read that star as hidden AI. Turnitin gives a different reason for hiding it.

What *% means: 1% to 19% AI 0:10

From 1 to 19 percent AI, Turnitin shows no number and highlights no sentences. Just the asterisk. Why hide it? To avoid false positives, Turnitin says. Below 20 percent, its guide adds, results are less reliable. A false positive is fully human writing flagged as AI. But it isn't zero either. The star means the detector flagged something, somewhere between 1 and 19 percent.

How the asterisk changed: 2023 vs 2024 0:36

Here's the twist. In May 2023, the star sat next to a number, added after testing found more false positives under 20 percent. Turnitin considered hiding those scores then, but teachers didn't like hidden AI percentages. In July 2024, it hid them anyway. A number under 20 with a star? That's an older report.

Where false positives land 0:57

Where do the false flags land? By Turnitin's 2023 figures, about 4 in 100 highlighted sentences may be human-written. Of those wrong sentences, 54 percent sat next to real AI writing. More hit the first and last few sentences, often your intro and conclusion, so Turnitin changed how it scores those. Mistakes piled up at the seams between human and AI text. Turnitin says its October 2026 update targets those seams, on new or resubmitted papers.

The under-1% false positive claim 1:28

That famous under 1 percent false positive rate? Turnitin only claims it for documents over 20 percent AI. In 2023, Turnitin's AI scientist David Adamson put it this way: "we expect we'll be wrong about one out of a hundred fully human written documents."

Universities that switched it off 1:44

Vanderbilt did the math in 2023: at 1 percent, about 750 of its 75,000 papers could have been wrongly labeled. Citing that and Turnitin's thin explanations, it switched the detector off. Curtin University in Australia turned it off too, from January 2026. At another Australian university, a student accused of using AI waited six months to be cleared, her transcript marked results withheld. That school says it threw out any case where Turnitin was the only evidence, and it dropped the tool in March 2025.

Can your teacher still say you used AI? 2:18

So can your teacher still say you used AI? Turnitin says that call is your teacher's, not the software's. Turnitin also says the score shouldn't be the sole basis for action. And an asterisk gives no sentence to point to. If you're questioned, ask to see the AI report; students don't see it by default. Turnitin tells teachers to weigh context and what they know about you. So bring context: your drafts, your notes, Turnitin's own rules.

So, should you worry? An asterisk isn't proof of AI; it's the zone Turnitin itself calls less reliable.

What the sources say

  • In Turnitin's AI writing report, *% means the detector's result fell between 1% and 19%. In that range Turnitin shows no numerical score and highlights no text, which it says is to avoid false positives, and its instructor guide adds that results below 20% are less reliable. Turnitin Help Center, Turnitin Guides
  • An asterisk is not the same as 0%. Turnitin's report guide lists 0% as its own result, while *% means the detector did flag some text as likely AI-written, but less than 20%. Turnitin Guides
  • In May 2023 Turnitin added an asterisk next to AI percentages under 20%, after its testing found a higher incidence of false positives below that level. Turnitin said it had considered hiding those scores, but educators did not like the idea of hidden AI percentages. Turnitin
  • Since a July 2024 release, Turnitin shows no number at all for results from 1% to 19%. Reports generated before that change can still show a number below 20% with an asterisk. Turnitin Guides
  • Turnitin's stated document false positive rate of less than 1% applies only to documents with over 20% AI writing. Turnitin describes that rate as possibly flagging about one in every 100 fully human-written documents. Turnitin, Turnitin Guides
  • By Turnitin's May 2023 figures, its sentence-level false positive rate was about 4%, meaning a highlighted sentence may be human-written about 4 times in 100. Turnitin said 54% of those wrongly flagged sentences sat right next to actual AI writing. Turnitin
  • Turnitin says it does not make a determination of misconduct and that the final decision rests with the instructor. Its FAQ also says the AI percentage should not be used as the sole basis for action or as a definitive grading measure. Turnitin Guides
  • Vanderbilt University disabled Turnitin's AI detector in August 2023. It noted that at a 1% false positive rate, around 750 of the 75,000 papers it submitted in 2022 could have been wrongly labelled as partly AI-written, and that Turnitin gave no detailed information on how the tool decides. Vanderbilt University
  • Curtin University in Australia switched off Turnitin's AI writing detection across all its campuses from 1 January 2026, while keeping Turnitin's text matching. Curtin University
  • Students do not see Turnitin's AI indicator by default. Turnitin's FAQ says only instructors and administrators see it, though instructors can download the AI report as a PDF and share it, and a newer Turnitin guide says instructors can make the report available to students. Turnitin's AI writing detection capabilities FAQs, Using the AI Writing Report

Sources

  1. Why is the AI Writing Detection report score showing as *%? Turnitin Help Center
  2. How to access the AI Writing Report Turnitin Guides
  3. Using the AI Writing Report Turnitin Guides
  4. AI writing detection model Turnitin Guides
  5. Turnitin's AI writing detection capabilities FAQs Turnitin Guides
  6. AI writing detection update from Turnitin's Chief Product Officer Turnitin
  7. Understanding false positives within our AI writing detection capabilities Turnitin
  8. Understanding false positives within Turnitin's AI writing detection capabilities Turnitin on YouTube
  9. Guidance on AI Detection and Why We're Disabling Turnitin's AI Detector Vanderbilt University
  10. Update on Turnitin AI detection tool Curtin University
  11. University wrongly accuses students of using artificial intelligence to cheat RNZ

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