Body Mass Index (BMI) is an easy-to-perform method of screening for weight categories. it can be considered an alternative to direct measures of body fat. In general, body Mass Index (BMI) is a person’s weight in kilograms divided by the square of height in meters. For children and teens, BMI is age- and sex-specific and is often referred to as BMI-for-age. In children, a high amount of body fat can lead to weight-related diseases and other health issues and being underweight can also put one at risk for health issue.