Can Grammarly Humanize AI Text? We Ran the Numbers
Grammarly fixes your grammar. It does not humanize AI text.
I keep seeing this question on Reddit and student forums. People assume that since Grammarly rewrites sentences, it must also make AI text undetectable. Those are two completely different things, and the test data confirms it.
What we tested
We ran 2,000 words of ChatGPT-4o output through every Grammarly feature available on a Premium account:
- Grammar corrections — accepted all suggestions
- Clarity rewrites — accepted every sentence rewrite offered
- Tone adjustments — set to "Casual" and "Confident"
- Full document rewrite — used Grammarly's AI assistant to rewrite sections
Then we checked each version against three detectors.
Results
| Grammarly Feature Used | GPTZero | Turnitin | Originality.ai |
|---|---|---|---|
| No Grammarly (raw AI text) | 96% AI | 94% AI | 92% AI |
| Grammar corrections only | 95% AI | 93% AI | 91% AI |
| Grammar + clarity rewrites | 91% AI | 89% AI | 88% AI |
| Grammar + clarity + casual tone | 89% AI | 87% AI | 85% AI |
| Full AI rewrite feature | 88% AI | 86% AI | 84% AI |
| Humanize AI Pro | 2% AI | 3% AI | 2% AI |
Even with every Grammarly feature applied, the text still scored 88% AI on GPTZero. That is only 8 points lower than the original.
Why Grammarly does not work for this
| What Grammarly Does | What a Humanizer Does |
|---|---|
| Fixes spelling errors | Restructures entire sentences |
| Improves grammar | Changes sentence length patterns |
| Suggests clearer phrasing | Breaks predictable transitions |
| Adjusts tone (formal/casual) | Alters statistical word distributions |
| Catches punctuation issues | Introduces natural burstiness |
Grammarly operates at the word and phrase level. Detectors operate at the document level. Fixing a comma splice or replacing "utilize" with "use" does not change the mathematical signature of your text.
Think of it like this: Grammarly is a copy editor. A humanizer is a ghostwriter who rewrites your work from scratch while keeping your ideas.
What about Grammarly's new AI features?
In 2025 and 2026, Grammarly added AI writing and rewriting capabilities. These features generate new text using Grammarly's own AI models. The problem:
Text generated by Grammarly's AI is just as detectable as ChatGPT text.
| Source | GPTZero Score |
|---|---|
| ChatGPT-4o | 96% AI |
| Grammarly AI-generated text | 93% AI |
| Claude 3.5 Sonnet | 82% AI |
Grammarly's AI features create more AI content. They do not humanize existing AI content.
The right way to use Grammarly in your workflow
Grammarly still has a place, just not as a humanizer:
- Write with AI (ChatGPT, Claude, etc.)
- Humanize with Humanize AI Pro
- Check grammar with Grammarly (catches any awkward phrasing from the humanization step)
- Verify with GPTZero or Turnitin
Grammarly is step 3, not step 2.
How this compares to actual humanizers
| Tool | Type | GPTZero Score After | Cost |
|---|---|---|---|
| Grammarly Premium | Grammar tool | 88% AI | $12/month |
| QuillBot | Paraphraser | 68% AI | $10/month |
| WordAI | Spinner | 51% AI | $57/month |
| Humanize AI Pro | Humanizer | 2% AI | Free |
The gap between a grammar tool (88%), a paraphraser (68%), and a real humanizer (2%) tells you everything.
Bottom line
Grammarly is a great grammar tool. Use it for grammar. Do not use it for humanization.
For humanization, use Humanize AI Pro. For grammar checking, keep using Grammarly. They are different steps in the same workflow.
Dr. Sarah Chen
AI Content Specialist
Ph.D. in Computational Linguistics, Stanford University
10+ years in AI and NLP research