What is BMI Calculator? BMI Calculator is free app that allows you to monitor BMI and percentage of fat in your body. Ideal weight - app calculates the ideal weight you should gain. To calculate it app uses the D. R. Miller formula. Body fat percentage is estimated from BMI by formula derived by Deurenberg and co-workers. All measurements use information about your body: gender, age, height and weight. App is designed for people of different ages and supports for both metric and imperial. Track your BMI and stay healthy!