The body mass index (BMI) is a way of estimating how much fat you have in your body based on your weight and height. However, BMI does not actually measure the percentage of body fat.
Why not calculate your BMI now? You simply take your weight in kilograms and divide it by the square of your height. For example, let's say you are 1.8 meters tall and weigh 80 kilograms. The square of 1.8 is 3.24. Divide 80 by 3.24 and you get 24.7. That is your BMI.