Body Mass Index

A formula called body mass index (BMI) can be useful in determining whether or not you're overweight. Basically, BMI is a height/weight ratio. For adults, according to the National Heart, Lung, and Blood Institute:

• a BMI of under 18.5 is considered underweight for adult men and women
• a BMI between 18.5 and 24.9 or less is considered normal weight in both men and women
• a BMI between 25 and 29.9 is considered overweight for adult men and women
• a BMI of 30 or above is considered obese in both men and women (Read about "Obesity")

You can use our calculator to determine your BMI. To check the results, or if the calculator won't work on your computer, just refer to this table. Again, NHLBI says that for both men and women, a BMI under 24 is considered healthy and a BMI of 30 or above is considered obese. It's important to remember, though, that BMI is only one measure of your health. Your percentage of body fat, your blood pressure, your resting pulse and many other factors need to be considered too. In addition, the American Council on Exercise says that people with higher muscle mass or bone density, such as athletes for example, may have a higher BMI, even though their bodies don't have extra fat. That's because BMI doesn't take body composition into account, so again, this is simply a tool. Always check with a qualified healthcare practitioner about your specific case.

Nevertheless, BMI can be helpful in determining if you do have a weight problem. And that's important. NHLBI says some 97 million adults in the United States are overweight or obese. Obesity and overweight substantially increase the risk of

• Hypertension (Read about "Hypertension")
• Type 2 diabetes (Read about "Diabetes")
• Heart disease (Read about "Coronary Heart Disease")
• Gallbladder disease (Read about "Gallstones")
• Osteoarthritis (Read about "Osteoarthritis")
• Sleep apnea (Read about "Sleep")
• Certain types of cancer (Read about "Cancer: What It Is")

Body Mass Index-for-Age (Children)

BMI is used differently with children than it is with adults, according to the Centers for Disease Control and Prevention (CDC). The same calculations are used to establish BMI but what it means is different. As children grow, their body fatness will change over the years. The interpretation of BMI depends on the child's age. Additionally, girls and boys differ in their body fatness as they mature. Therefore, BMI-for-age is plotted on gender-specific growth charts. Each of the BMI-for-age gender specific charts contains a series of curved lines indicating specific percentiles. So after you calculate the BMI number, you need to open either the BMI chart for girls or the BMI chart for boys.

Note: You need Javascript to use some of the features in this article.

Find your child's age on the horizontal border, and their BMI number (from the calculator) on the vertical borders. Then, plot where these lines intersect. This will show you what percentile they are in. Children over the age of two are considered:

• underweight if their BMI falls below the 5th percentile
• at a healthy weight if their BMI falls between the 5th and the 85th percentiles
• at risk for being overweight if their BMI is in the 85th to 95th percentile
• overweight or obese if their BMI is at or higher than the 95th percentile

BMI decreases during the preschool years, then increases into adulthood. The percentile curves reflect this pattern of growth. (Read about "Childhood Weight Issues")

If you have concerns you should discuss them with your child's doctor.