The performance score is an indicator of how accurate your document is compared to documents written by other Grammarly users who set the same goals you did.
To calculate the performance score, Grammarly calculates the accuracy level of your document based on the total word count, and the number and types of writing issues detected. Then, Grammarly compares the accuracy level of your document to the accuracy levels of all other documents where users set the same goals. A score of 90, for example, means that the writing in your document is more accurate than the writing in 90 percent of other documents with similar goals.
To access your performance score, open any document in the Grammarly Editor and click Overall score:
This menu also allows you to check the document statistics, such as readability score, word count, and vocabulary use.
To learn more about this feature, please check out this article.