If you care about your health, you should maintain normal weight. Use BMI Calculator to find out your Body Mass Index, which reveals if you are underweight, normal, overweight or obese. You can use it on your home computer. To find out your BMI, select English or Metric system, insert your height, weight and then click the Calculate button. The result will appear at once. BMI Calculator is designed for adults aged twenty years and above. The BMI formula for children and teens differs from the one for adults.