Calculate Body Mass Index

Three boys play basketball

For adults, a healthy weight is defined as the appropriate body weight in relation to height. Body Mass Index (BMI) is calculated from your height and weight and is a useful measure of overweight and obesity. People who are overweight (BMI of 25 to 29.9) have too much body weight for their height.

People who are obese (BMI of 30 or above) almost always have a large amount of body fat in relation to their height. There are exceptions, of course. Big athletes with lots of muscle might have a BMI over 30, but may still have a healthy body composition. They would not be considered obese from the perspective of health risk.

Use a BMI calculator for adults and learn your BMI by entering your height and body weight. Or use the BMI tables on the Aim for a Healthy Weight website.

BMI for Children

For children and teens, overweight is defined differently than it is for adults. Children are still growing, and boys and girls develop at different rates. So, BMI for children 2 to 20 years old is determined by using a BMI chart that compares their weight and height along with growth charts. The growth charts use a child's BMI, age, and sex to produce a BMI percentile.

A child's BMI percentile shows how his or her BMI compares with other boys or girls of the same age. A child or teen that is between the 85th and 95th percentile on the growth chart is considered at risk of overweight. A child or teen that is at the 95th percentile or above is considered overweight. For children, BMI is used to screen for overweight, healthy weight, or underweight. For example, a child may have a high BMI for age and gender, but to determine if excess fat is a problem, a health care provider would need to perform further assessments.

A BMI percentile will not tell you if your child has or will get a disease. However, you should ask your family doctor, pediatrician, or other health care provider about your child's BMI percentile and whether they are at risk for disease. For more information about BMI percentile and growth charts for children, visit disclaimer.

Last Updated: February 13, 2013