BMI is an estimate of your body fat, based on your height and weight. While it is generally accurate and easy to calculate, BMI can read too high for athletes or others with large, heavy muscles. It can also exaggerate low readings for seniors who have lower muscle mass. Although it is not a perfect diagnostic tool when used alone, a high BMI indicates risk for heart disease, diabetes, cancer, high blood pressure and osteoarthritis. For all adults aged 20 years or older, BMI falls into one of these categories:

• Underweight - Less than 18.5
• Normal - 18.5 to 24.9
• Overweight - 25.0 to 29.9
• Obese - 30.0 and higher

BMI calculations are slightly more complicated in evaluating youths age 2 to 20. Youth's body fat levels change as they grow, decreasing during preschool years, then increasing into adulthood. Also, boys and girls differ in their body fat as they mature. This is why BMI for youths, also referred to as BMI-for-age, is gender- and age-specific. Each of the BMI-for-age charts contains a series of curved lines indicating specific percentiles that reflect these growth patterns. For example, a child who has a BMI score at the 60th percentile means that 60 percent of American children of the same gender and age have a lower BMI. The following percentile ranges are used to identify underweight and overweight in children:

• Underweight - Equal to or less than;) 5th percentile
• At risk for Overweight - 85th to 94th percentile
• Overweight - Equal to or more than 95th percentile