BMI is a simple calculation using your height and weight. It is calculated as BMI= your weight (Kg) / square of height (metres). It is generally used to indicate whether a person has a healthy body weight for their height. BMI applies to most adults between 18 and 65 years.
A BMI between 18.5 and 24.9 is considered healthy, BMI between 25 and 30 is overweight, and BMI over 30 is considered obese.
Though BMI is widely used, it does have limitations because it is a measure of excess body weight and not body fat. So even if you have a healthy weight you may have excess body fat if you have a sedentary lifestyle. On the other hand a person with the same BMI with more muscular composition would be considered healthy.