Your Performance score tells you how accurate your document is compared to documents written by other Grammarly users who set the same goals you did.
For example, imagine you open a document in the Grammarly Editor and choose the goals "Tell a Story" and "Informal." 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 chose the goals "Tell a Story" and "Informal." The Performance score you see tells you how your document compares to these other documents. 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.