It is important to know BMI, or body mass index, to get a relative idea of the amount of fat in the body, which affects overall health. BMI is a widely accepted screening tool used by medical professionals because it is simple and inexpensive, according to WebMD. While it is a useful screening tool, it is not a diagnostic tool and should be used with other assessments to determine health risks of being overweight.
A BMI calculator divides weight in kilograms by height in meters, notes the Centers for Disease Control and Prevention. This produces a general calculation of body fat. A person's BMI falls into one of four general categories: underweight, normal weight, overweight or obese. Individuals falling in the overweight or obese categories often have a higher risk of metabolic problems and diseases.
An unhealthy BMI is an indicator that the individual needs to make health changes and possibly see a physician. When BMI is high, a physician may perform additional testing, including dietary and exercise evaluations, family history, and screenings for health problems, states the CDC. Obesity increases the risk for several conditions including certain cancers, heart disease, stroke, Type 2 diabetes, high cholesterol and mental illness.
While BMI provides a general idea of body fat, it does leave some room for error. BMI does not factor in gender differences, age and muscle mass, says WebMD. This means an athlete with lots of lean muscle may have a high BMI even though he has low body fat.