91st percentile represents the value of the 91st rank in a given set of data. Percentile value is represented as R, and is given as R = 0.91x (N+1) where, R is the percentile rank and N is the number of data. This page provides you the 91st Percentile formula to calculate the 91st percentile for your desired data set. This is a simple formula to calculate the 91st percentile. Use this simple data analysis statistics formula to solve your Percentile related problems.