Grammarly AI Detector vs Turnitin: AI detector comparison
A side by side look at pricing, methodology, language support and best-fit use case. Every claim on this page is linked to a source at the bottom.
Last updated . Reviewed by IsItAI Editorial.
At a glance
Grammarly AI Detector
US, 2009 (AI detector 2024)Detection layered onto Grammarly's writing assistant.
- Pricing
- Bundled in Grammarly Pro from $12/month
- Free tier
- Free tier with limits
- API
- No
- Languages
- 1
Turnitin
US, 1998 (AI detection added 2023)Institutional plagiarism and AI detection bundled into LMS workflows.
- Pricing
- Institution-licensed, around $3 per student/year
- Free tier
- No free tier (institutional only)
- API
- No
- Languages
- 30
Side by side
| Feature | Grammarly AI Detector | Turnitin |
|---|---|---|
| Free tier | Free tier with limits | No free tier (institutional only) |
| Starting price | Bundled in Grammarly Pro from $12/month | Institution-licensed, around $3 per student/year |
| Cost per 1k words | Bundled | Not directly comparable |
| API available | No | No |
| Languages supported | 1 | 30 |
| Founded | 2009 (AI detector 2024) | 1998 (AI detection added 2023) |
| Country | US | US |
| Primary audience | Existing Grammarly users | Schools and universities at institutional scale |
| Best for | Existing Grammarly users wanting a one-click sanity check | Universities and schools that already license Turnitin for plagiarism |
| Known weakness | English only and not the main product | Not available to individual students or teachers, no public methodology |
How each tool works
Grammarly AI Detector
Method: Detector added 2024 inside the Grammarly editor. English only.
Data handling: Stores submissions per Grammarly's main privacy policy.
Turnitin
Method: Classifier layered onto the existing plagiarism similarity engine. Methodology not published in peer-reviewed venues.
Data handling: Stored in institutional Turnitin repository per the school's licence agreement.
How accurate are AI detectors? What the research says
Two findings from independent academic research apply to almost every detector on this list, including Grammarly AI Detector and Turnitin.
1. False positives on non-native English writers. Liang et al. (Stanford, 2023) found that GPT detectors flagged over half of TOEFL essays written by non-native English speakers as AI-generated, while flagging almost none of the essays from US students. If your use case involves non-native English writers, never treat a detector verdict as proof on its own.
2. Paraphrasing reliably defeats classifiers. Sadasivan et al. (Maryland, 2023) showed that running AI output through a paraphraser drops detection performance close to chance. Both Grammarly AI Detector and Turnitin are vulnerable to this.
For a deeper breakdown of how accuracy claims hold up across 2026 testing, see our guide to how accurate AI detectors actually are in 2026.
Where Grammarly AI Detector wins
- Available to individuals, where Turnitin is institution-only and a student cannot access it directly.
- One-click check inside the Grammarly editor you may already use, bundled in Grammarly Pro from $12 per month.
Where Turnitin wins
- It is the system your institution actually grades against, layered onto the plagiarism engine schools already license.
- Covers 30 languages versus Grammarly's English only.
Which one should you pick, Grammarly AI Detector or Turnitin?
These are not really rivals. Grammarly's detector is a self-check for individual writers, while Turnitin is the institutional system your submission is measured against, and you cannot choose it as a student. Use Grammarly or a dedicated detector to sanity-check before submitting, but the two use different classifiers, so a clean result in one does not predict the other. Turnitin's AI detector was publicly disabled by Vanderbilt University in 2023 over accuracy concerns, so no single flag should be treated as proof.
Frequently asked questions
Is Grammarly AI Detector free?
Free tier with limits
Is Turnitin free?
No free tier (institutional only)
Can either tool be fooled by paraphrasing?
Yes. Sadasivan et al. (2023) demonstrated that paraphrasing reliably defeats most AI classifiers. Treat any detector verdict as a screening signal, not proof.
Are AI detectors fair to non-native English writers?
Independent research (Liang et al. 2023) found high false-positive rates for non-native English writing. Always combine a detector signal with other evidence, never use it as a sole basis for an academic or hiring decision.
Which one should I pick if I have to choose one, Grammarly AI Detector or Turnitin?
These are not really rivals. Grammarly's detector is a self-check for individual writers, while Turnitin is the institutional system your submission is measured against, and you cannot choose it as a student. Use Grammarly or a dedicated detector to sanity-check before submitting, but the two use different classifiers, so a clean result in one does not predict the other. Turnitin's AI detector was publicly disabled by Vanderbilt University in 2023 over accuracy concerns, so no single flag should be treated as proof.
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Sources and further reading
- Grammarly AI checker
- Turnitin AI writing detection page
- Vanderbilt University guidance on disabling Turnitin's AI detector (2023)
- Liang et al. (Stanford, 2023): GPT detectors are biased against non-native English writers
- Sadasivan et al. (2023): Can AI-generated text be reliably detected?