Does Turnitin Detect AI?

How Turnitin’s AI detector works

Turnitin’s AI detection looks for the statistical fingerprints language models leave behind. The two strongest signals are perplexity — how predictable each word is given the ones before it — and burstiness — how much sentence length varies. AI text tends to be low on both: smooth, even, and predictable.

It returns an overall percentage estimate of how much of the document reads as AI-generated, not a sentence-by-sentence verdict you can fully audit.

What actually gets flagged

Writing that is uniformly structured, leans on stock transitions (“moreover”, “in conclusion”), and avoids concrete, specific detail is the most likely to be flagged. That describes a lot of raw AI output — but also some careful human writing, especially from non-native English writers.

How reliable is it?

Detection is probabilistic. Turnitin itself frames its score as an indicator, not proof, and independent testing has shown both false positives (human flagged as AI) and false negatives (AI passing as human). Treat any single score as a signal to look closer, not a verdict.

What to do if your writing is flagged

If you wrote it yourself, keep your drafts and version history — they are the strongest evidence. If you drafted with AI and want it to read like you, rewrite it so sentence length varies and the stock phrasing is gone, then check it. Humanit’s AI humanizer does the rewrite and its built-in detector lets you verify the result before you submit.