Want to quickly assess whether your weight is healthy? The Body Mass Index app will help you calculate your BMI in seconds. It's a free and easy-to-use tool for anyone monitoring their health, planning to lose weight, or simply wanting to learn more about their body. How does it work? Body Mass Index is a measure of how well a person's weight corresponds to their height. Simply enter two parameters, and the app will use a formula to determine your weight category: underweight, normal, overweight, or obese.