Body mass index (BMI) is a widely used tool for estimating body fat based on your height and weight. While it doesn’t directly measure body fat, BMI can help start to identify whether you are underweight, within a healthy weight range, or living with overweight or obesity.

Healthcare providers frequently use BMI as a screening measure, not a diagnostic one. Meaning, a BMI score can suggest whether you may be at risk for certain health conditions, particularly those related to weight (e.g. type 2 diabetes, cardiovascular disease). It can also help providers determine whether you qualify for prescription weight loss treatments like  Zepbound or Wegovy.

However, BMI doesn’t provide a full picture of your health. It doesn’t account for muscle mass, bone density, or fat distribution—all of which can influence health outcomes independently of BMI. Biological sex, age, and ethnicity are also not factored into BMI, despite being key predictors of body composition and disease risk.

That said, BMI can still be a helpful starting point. Large studies have found that BMI is strongly associated with the risk of developing conditions like type 2 diabetes, heart disease, and certain cancers, especially when considered alongside other markers like waist circumference and metabolic health indicators.

BMI is calculated by dividing your weight in kilograms by your height in meters squared (kg/m²).

BMI = weight (kg) ÷ height² (m²)
BMI = [weight (lb) ÷ height² (in²)] × 703

BMI measurements are typically divided into four main categories: underweight, normal, overweight, and obesity. Obesity is further broken down into three classes. These classifications are based on BMI ranges defined by the Centers for Disease Control and Prevention (CDC), and they apply to adults aged 20 and older:
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These categories do not apply to children, teens, or pregnant individuals. They also may not tell the full story or accurately reflect health risk for all adults.

BMI doesn’t distinguish between muscle and fat, nor does it account for fat distribution, particularly visceral fat, which is more strongly associated with cardiometabolic risk. For this reason, many healthcare providers also look at other metrics, such as waist circumference, lifestyle factors, and metabolic labs, when assessing weight and overall health.

Once you calculate your BMI, it will fall into one of the standard categories: underweight, normal weight, overweight, or obesity. These categories offer a general sense of how your weight may relate to your risk for certain health conditions.​

Keep in mind that BMI is just one piece of the puzzle. While it may flag potential health risks, it doesn’t explain why someone may fall into a given category or what could be happening beneath the surface. That’s where a closer look at other health indicators becomes important.

We’ve mentioned it before, but it’s worth emphasizing: BMI may have its uses, but it doesn’t account for everything that matters when it comes to your health.

So, what isn’t your BMI telling you?

Think of your BMI range as a starting point—not a verdict. On its own, BMI can’t tell you everything about your health, but it can offer a useful frame of reference for deeper conversations with your healthcare provider.

If your BMI falls in the normal range, it suggests that your weight is less likely to be associated with certain chronic conditions. But it’s still important to pay attention to other markers like blood pressure, cholesterol, energy levels, and overall wellbeing.

If your BMI is in the underweight, overweight, or obesity range, that doesn’t automatically mean you’re unhealthy or need to make drastic changes. But it may be a sign to take a closer look at your lifestyle, eating habits, physical activity, and other health metrics. In some cases, a higher BMI may make you eligible for medical support like prescription weight loss medications (i.e. pills or injections) or clinical care programs.

No matter your number, the most helpful next step is to speak with a healthcare provider who can evaluate the full picture—your goals, lab work, family and personal medical history, mental health, and more—and help you decide what makes sense for you and your body.