I tried out your calculator two different ways knowing my body fat composition (I was measured on a body fat scale at my gym). On the first trial I entered data using my body fat percentage, which had been measured to be 6%. I weigh 87 pounds and the calculator told me this weight was within healthy range for me. Considering the fact that I am 5 feet 3 inches tall, I know many doctors and nurses who have very recently told me I need to gain weight. (By the way, I am a recovered anorexic and I think your calculator could give people like myself the wrong idea!!!) I entered the data on a second trial without entering my body fat percentage and it said I am underweight. Well, which is it? You tell me!