BMI Prime

BMI Prime, which is a simple modification of the BMI system, is the ratio of actual BMI to upper limit BMI 

As defined, BMI Prime is also the ratio of body weight to upper body weight limit, calculated at BMI 25.

Individuals with BMI Prime less than 0.74 are underweight; those between 0.74 and 0.99 have optimal weight; and those at 1.00 or greater are overweight. 

Wikipedia