Understanding Body Mass Index

BMI stands for Body Mass Index. It is important to know what your BMI does and does not indicate about your weight, health and lifestyle choices. Your BMI is calculated from your height and weight. It is a fairly reliable indicator of body fat for most adults, with athletes and the elderly being two exceptions. BMI is an inexpensive alternative to direct measurements of body fat, such as underwater weighing, but it is only one of many factors that you and your health-care provider should use in evaluating your health status.

Calculating Your BMI

You can calculate your BMI with this formula: weight (in pounds) / [height (in inches) x height (in inches)] x 703 or use the Academy BMI calculator.

The Centers for Disease Control and Prevention uses BMI to define terms like overweight and obese: 

• Underweight: BMI below 18.5
• Normal weight: 18.5 to 24.9
• Overweight: 25.0 to 29.9
• Obese: 30.0 and above.

BMI and Your Health

People with very low or very high BMIs tend to have the greatest health risks. Even so, BMI is only one factor in your overall health. For example, if your BMI falls into the normal weight category, you will still have a higher risk of health problems if you:

• Smoke cigarettes
• Do not participate in regular physical activity
• Eat lots of nutrient-poor foods with added fat and sugar.

If your BMI is in the overweight category, you will have a lower overall health risk if you:

• Get regular physical activity
• Have blood pressure, blood sugar and cholesterol levels that are within normal limits.

This means BMI is one aspect of your health to discuss with your care provider. Together, you can decide if other assessments need to be done and whether lifestyle changes such as eating smarter and moving more will improve your health.

BMI Measurements in Children and Teens

While BMI calculations for children and teens use the same formula as adults, criteria used to define obesity and overweight are different for young people because of factors like body fat differences between boys and girls and variations in body fat at different ages. Visit the BMI Percentile Calculator for Child and Teen to determine your child's BMI.