Calculating your body mass index (BMI) is often part of a routine health checkup. But in recent years, debate has grown as to whether doctors should use BMI for individual health assessment.

Here's why your doctor may or may not use BMI — and what they may use instead.

How Is BMI Calculated?

BMI is your weight in kilograms divided by the square of your height in meters.

The equation is BMI = weight (kg) / height (m) 2 .

If you're an adult age 20 or older, you can use the Centers for Disease Control and Prevention's (CDC) Adult BMI Calculator to find your BMI and the related BMI category.

Adult BMI categories

Based on your BMI calculation, you'll fall into one of four main BMI weight categories:

  • Underweight — Less than 18.5.
  • Healthy weight — 18.5 to less than 24.9.
  • Overweight — 25 to less than 30.
  • Obesity — 30 or greater.

Obesity also has three subcategories:

  • Class 1 obesity — 30 to less than 34.9.
  • Class 2 obesity — 35 to less than 40.
  • Severe obesity — 40 or greater.

Why Is BMI Important?

BMI is a health assessment tool used worldwide. The benefits of BMI are that it's a quick, easy, free way to check your weight health.

If your BMI places you in the overweight or obesity categories, you're at an increased risk of chronic or serious health problems, including:

Women in these BMI categories also face an increased risk of fertility issues and pregnancy problems, including gestational diabetes and preeclampsia.

Likewise, having an underweight BMI classification can also point to health problems, such as eating disorders or gastrointestinal health issues.

Major organizations that use BMI include the CDC, the National Institutes of Health, the World Health Organization, and the American Society for Metabolic and Bariatric Surgery.

How does BMI relate to overall health?

BMI is just one measure of health. Doctors may use BMI to:

  • Screen for obesity.
  • Measure the progress of weight management and weight loss interventions.
  • Decide who can receive medical treatment for weight loss. This includes medically supervised diet and exercise interventions, weight loss medications, and bariatric surgery. Health insurance companies often require BMI as part of treatment criteria.

Is BMI a reliable health metric?

It depends on how you use it.

In large-scale population studies, BMI has proved useful in predicting overall mortality based on body fat, according to a 2025 review published in Surgery for Obesity and Related Diseases .

Localities, states, and public health entities use BMI data to make decisions to improve the health of populations. The CDC bases its adult obesity maps, which show obesity rates by U.S. state or territory and by race/ethnicity, on BMI data.

Though BMI is also helpful as a primary health screening tool, it has its limits when it comes to predicting health outcomes for chronic diseases on an individual basis. That's according to a 2024 report on the advantages and limitations of BMI in the International Journal of Environmental Research and Public Health.

What Are the Limitations of BMI?

Using BMI to assess personal health has long courted controversy.

Until the 2010s, most doctor visits didn't include BMI calculations. That's according to a 2023 report in the American Medical Association (AMA) Journal of Ethics . After the American Medical Association declared obesity a disease in 2013, more doctors started using BMI to screen for obesity.

This may surprise you, but BMI isn't a direct measure of body fat. Instead, BMI provides a rough estimate of the amount of fat in your body.

BMI also can't tell:

  • The difference between fat, muscle, and bone mass — all of which affect your weight. According to NIH, BMI may overestimate body fat in athletes and people with a muscular build. It may also underestimate fat in those who have lost muscle, including older adults.
  • What types of excess fat you have in your body.
  • Where in your body you carry excess fat. People who carry excess fat in their waist are at a higher risk of heart disease and type 2 diabetes, compared to those who carry it in their hips. This risk increases with a waist size greater than 35 inches for women or greater than 40 inches for men, according to NIH.

Standard BMI calculators also take a one-size-fits-all approach. They base category cutoffs primarily on health risks in non-Hispanic White populations. They don't account for race, ethnicity, or sex subgroups, which all factor into personal health risks.

For these and other reasons, the AMA's Council on Science in Public Health proposed removing BMI as a standard measure in 2023.

Are There Alternatives to BMI for Health Awareness?

BMI alone provides an incomplete picture of your personal health and health risks. For a more holistic health assessment, the CDC currently recommends using BMI with other health evaluations. These include:

  • Health history — Including your current health conditions and your family medical history.
  • Lifestyle behaviors — Such as your diet, physical activity, and sleep.
  • Physical exam — Including checks of blood pressure and muscle mass.
  • Testing — Like blood tests for metabolic indicators, such as high blood sugar and high cholesterol.

A more holistic view of weight and weight-related health may replace BMI soon. In January 2025, a global commission of 58 experts issued a report in The Lancet Diabetes & Endocrinology Journal calling for a more precise definition and diagnostic criteria of obesity.

They argued that BMI's only effective uses are to measure, screen for, and study population-wide health risks. It shouldn't serve as an individual measure of health.

The new criteria could change who has access to medical treatment for obesity. Whether and how soon doctors and other health care providers start using these new guidelines is still forthcoming. To date, over 75 organizations worldwide have endorsed the new criteria. These include the American Diabetes Association, the American Heart Association, and the Obesity Society.

If you're feeling concerned about your weight or health risks, talk to your doctor about what tools — besides BMI — make sense for you.