Calculate Your Body Mass Index. Body mass index (BMI) is a measure of body fat based on height and weight that applies to adult … Body Mass Index (BMI) Information about how BMI is a screening, individual health, and population health measure. BMI calculator online: Get your Body Mass Index results fast. Check if you're underweight, normal, overweight, or obese. It's free! This calculator provides BMI and the corresponding BMI category for adults 20 and older. For children and teens 2 through 19, use … Submit your height and weight to calculate your BMI. Complete optional fields below to learn more about your waist size, health risks, …