Aubrey Bailey, PT, DPT, CHT  is a physical therapist with over 20 years of experience in a variety of healthcare settings.

Anita Chandrasekaran, MD, MPH, is board-certified in internal medicine and rheumatology and currently works as a rheumatologist at Hartford Healthcare Medical Group in Connecticut.

Body mass index (BMI) is an estimate of body fat that is based on your weight and height. This calculation helps determine whether you are underweight, at a healthy weight, overweight, or obese.

BMI can be used to assess your risk for developing certain health problems. For example, people in higher weight categories are considered to be at greater risk for high blood pressure and high cholesterol.

However, the calculation has its limitations. Namely, BMI doesn't take into account age, assigned sex, race, or muscle mass.

This article discusses BMI, how it is calculated, its pros and cons, and alternatives for assessing potential health risks.

BMI is calculated by dividing your body weight in kilograms by your height in meters squared.

BMI can also be calculated by dividing your weight in pounds by your height in inches squared, then multiplying the answer by 703.

You may not have all of these numbers at the ready. Online BMI calculators can do the work for you.

Body mass index scores are broken down into the following categories:

Obesity is sometimes broken down into additional categories:

BMI is calculated by dividing weight by height. It’s one way healthcare providers assess the health risks associated with weight—both too little or too much.

Excess body fat has been linked to increased risk of a number of health issues. BMI scores in the overweight and obese categories can indicate that a person is at higher risk of certain diseases, such as:

On the plus side, BMI is a simple way to estimate body fat. It’s convenient, inexpensive, and can be used routinely. As a result, it’s an easy way to identify someone who may have a health risk worth looking into. It’s also used universally by medical professionals in research around the world.

However, it also has significant limitations. To start with, it can't be used to diagnose health issues—just identify possible red flags.

It can also be a false alarm for a significant number of people due to the following factors that BMI does not account for.

Muscle and bone are denser than fat. Since the only measures used to calculate BMI are weight and height, it can overestimate body fat in athletes or individuals with lots of muscle mass.

It can also underestimate body fat in people with very little muscle mass.

BMI does not account for a person's race, which can influence weight-related health risks and body composition, the amount of body weight that is made up of fat versus lean muscle tissue.

On average, for example, Asians and South Asians have greater proportional body fat than Europeans at the same weight, while Blacks have less body fat and more muscle at the same weight as compared to Europeans.

For this reason, some experts now argue for tailored cutoffs for specific groups.

Those born female tend to have more body fat in comparison to men. BMI doesn’t account for this difference. Therefore, a woman may register in a “safe” category of BMI but still have levels of body fat that can represent a health risk.

Normal BMI ranges may not accurately predict health risks for the young and old. For example, in the elderly, a BMI below 23—which is in the so-called normal range for adults—is associated with higher mortality, while being in the “overweight” range is not.

Evidence suggests that where body fat is located also matters. Those who carry weight around the middle—what's called an “apple” body shape—have higher health risks than people with a "pear" shape (i.e., those who accumulate weight in the hips and thighs).

Some have called for retiring BMI because of these issues. While its disadvantages are widely accepted, BMI remains in use partly because it’s simple to use.

When desired or considered necessary, other methods for measuring body fat or assessing your health risk can be used in place of, or in addition to, BMI.

More sophisticated methods of measuring body fat and composition also exist. However, most are not available in standard medical offices. Instead, they’re used in specialist or research settings.

BMI is not the only way to assess body fat or the risks associated with weight. Health risks can also be estimated by looking at waist circumference as well as its relationship to hip circumference. Body fat can be calculated with skin-fold testing, by using a smart scale, or via several other methods.

It's possible that you could have a normal BMI but still have heightened health risks.

For example, maybe your BMI is in the normal range, but you are not physically active, your diet is poor, you have a family history of disease, or you smoke—any of which can affect your risk of a host of health concerns.

A senior adult could have a normal BMI, but have significant health issues like hardening of the arteries (atherosclerosis).

And, as discussed, it's possible that your BMI could be in the healthy range, but your race, age, sex, or another factor make that measurement less accurate in your case.

Consider BMI for what it is—an estimate, not a measurement, and just one piece of information that can help paint the picture of your overall health. Your healthcare provider can help you better understand how your BMI fits in.

BMI provides an estimate of your body fat, which can influence your risk of developing diseases. Calculating BMI is quick, and free BMI calculators are available online.

However, BMI has a number of limitations. This measure does not take into account your age, race, sex, or fitness level.

In addition, multiple factors need to be considered when determining what a healthy weight is for you. BMI can provide one small piece of information, but it should not be the only resource used when deciding how much you should weigh to stay well.

BMI is an estimate of body fat, but it is not an accurate way to determine specific body fat percentages.

Adult BMI measurements are not based on someone's sex.

Assessing body composition—amount of body fat versus lean muscle tissue—is a more accurate way to determine your overall health risks.

Being healthy is about more than just a number on the scale. Talk to your healthcare provider to determine your recommended weight range while considering other factors that influence overall health.

Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life.

Thank you, {{form.email}}, for signing up.

There was an error. Please try again.

Centers for Disease Control and Prevention. Defining adult overweight and obesity.

National Heart, Lung, and Blood Institute. BMI tools.

Provencher MT, Chahla J, Sanchez G, et al. Body Mass Index Versus Body Fat Percentage in Prospective National Football League Athletes: Overestimation of Obesity Rate in Athletes at the National Football League Scouting Combine. J Strength Cond Res. 2018 Apr;32(4):1013-1019. doi:10.1519/JSC.0000000000002449

Harvard School of Public Health. Obesity Prevention Source. Ethnic Differences in BMI and Disease Risk.

Harvard Health Publishing. How useful is the body mass index (BMI)?

Golzarri-Arroyo L, Mestre LM, Allison DB. What’s New in Understanding the Risk Associated With Body Size and Shape? Pears, Apples, and Olives on Toothpicks. JAMA Netw Open. 2019;2(7):e197336. doi:10.1001/jamanetworkopen.2019.7336

National Heart, Lung, and Blood Institute. Assessing your weight and health risk.

Zhu S, Heymsfield SB, Toyoshima H, Wang Z, Pietrobelli A, Heshka S. Race-Ethnicity-Specific Waist Circumference Cutoffs for Identifying Cardiovascular Disease Risk Factors. Am J Clin Nutr. 2005 Feb;81(2):409-15. doi:10.1093/ajcn.81.2.409

Harvard Health Publishing. Why worry about your waistline?

Lemos T, Gallagher D. Current body composition measurement techniques. Curr Opin Endocrinol Diabetes Obes. 2017;24(5):310-314. doi:10.1097/MED.0000000000000360

Vasconcelos Fde A, Cordeiro BA, Rech CR, Petroski EL. Sensitivity and specificity of the body mass index for the diagnosis of overweight/obesity in elderly. Cad Saude Publica. 2010 Aug;26(8):1519-27. doi:10.1590/s0102-311x2010000800006

Thank you, {{form.email}}, for signing up.

There was an error. Please try again.