BMI Calculator

---

What is BMI?

Body mass index (BMI) estimates body fat from your height and weight. It does not measure fat directly, but it helps identify whether you are underweight, at a healthy weight, or living with overweight or obesity. Providers use it as a screening measure, not a diagnosis, to flag possible risk for weight-related conditions like type 2 diabetes and cardiovascular disease, and to help determine whether you may qualify for prescription weight loss treatments like semaglutide or tirzepatide.

BMI does not capture the full picture. It does not account for muscle mass, bone density, fat distribution, sex, age, or ethnicity, all of which affect health independently. Even so, large studies link BMI strongly to the risk of type 2 diabetes, heart disease, and certain cancers, especially alongside markers like waist circumference and metabolic labs, which makes it a useful starting point.

How the BMI Calculator Works

BMI is your weight divided by the square of your height. The metric and imperial formulas give the same result:

BMI falls into four main categories: underweight, normal, overweight, and obesity, with obesity split into three classes. These ranges come from the Centers for Disease Control and Prevention (CDC) and apply to adults aged 20 and older.

Category	BMI Range
Underweight	Below 18.5
Normal	18.5 to 24.9
Overweight	25 to 29.9
Class 1 obesity	30 to 34.9
Class 2 obesity	35 to 39.9
Class 3 obesity	40 and above

These categories do not apply to children, teens, or pregnant individuals, and may not fully reflect risk for every adult. Because BMI ignores muscle versus fat and where fat sits (visceral fat carries higher cardiometabolic risk), many providers also weigh waist circumference, lifestyle, and metabolic labs.

What does my BMI number mean?

Your BMI falls into one of the standard categories below, each giving a general sense of weight-related health risk.

• Underweight (below 18.5): Being underweight can be associated with increased risks of malnutrition, weakened immune function, osteoporosis, and, especially among older adults, higher mortality risk.
• Normal weight (18.5 to 24.9): This range is generally considered to carry the lowest overall risk of chronic disease.
• Overweight (25 to 29.9): Individuals in this category may be at elevated risk for high blood pressure, insulin resistance, and heart disease, especially when paired with other risk factors like excess abdominal fat.
• Class 1 obesity (30 to 34.9): This level can be associated with significantly increased risks for type 2 diabetes, cardiovascular disease, and sleep apnea.
• Class 2 obesity (35 to 39.9): Often associated with greater cardiometabolic risk, reduced mobility, and liver disease.
• Class 3 obesity (40 and above): Tends to carry the highest risk for serious chronic conditions, including those above as well as certain cancers.

BMI is just one piece of the puzzle. It can flag risk but does not explain why you fall into a category or what is happening underneath, which is where other health markers come in.

What does my BMI not tell me?

BMI has its uses, but it does not account for everything that matters for your health. Here is what your BMI number leaves out:

• How much of your weight is muscle versus fat. BMI does not distinguish between lean mass and body fat, so a very muscular person such as an athlete may be classified as having overweight or obesity even with low body fat and otherwise optimal health markers.
• Where fat is stored in your body. Fat concentrated in the abdomen (visceral fat) can pose a greater health risk than fat elsewhere. Two people with the same BMI may have very different body compositions and risk levels.
• Your metabolic health. BMI says nothing about blood pressure, cholesterol, blood sugar, or inflammation.
• Your fitness level. BMI does not reflect physical fitness. Research suggests people with higher BMIs who are fit can be healthier than those with lower BMIs who do not exercise.
• Your age, sex, or genetics. These influence body composition and risk but are not part of the calculation. Women, for example, carry more total body fat than men at the same BMI.
• Your race and ethnicity. BMI categories were derived largely from white populations. Some research suggests, for example, that people of Asian descent may develop weight-related conditions at lower BMIs, which is why some experts argue for ethnicity-adjusted thresholds.
• Your habits and lifestyle. How you eat, sleep, and manage stress all affect your weight and health but are not captured by BMI.

How to use your BMI range

Think of your BMI as a starting point, not a verdict. It is a useful frame of reference for a deeper conversation with a provider, not the final word on your health.

A normal-range BMI suggests lower risk of certain chronic conditions, though markers like blood pressure, cholesterol, and energy still matter. A BMI in the underweight, overweight, or obesity range does not automatically mean you are unhealthy, but it is a signal to look closer at your lifestyle and health metrics. In some cases, a higher BMI may make you eligible for medical support such as prescription weight loss medication.

BMI and GLP-1 weight loss eligibility

BMI is the primary number that determines eligibility for GLP-1 medications like semaglutide and tirzepatide. The widely accepted thresholds are a BMI of 30 or higher, or a BMI of 27 or higher when paired with a weight-related condition such as type 2 diabetes, high blood pressure, high cholesterol, or sleep apnea.

Meeting the threshold opens the door, but it is not the whole evaluation. The Tactus Health team reviews your full health history, current medications, and lab work where clinically indicated before recommending a protocol. Medications also differ in expected outcomes: in clinical trials, semaglutide produced an average 14.9 percent body weight reduction (STEP 1) and tirzepatide an average 20.9 percent reduction (SURMOUNT-1). Individual results vary. The best next step is a provider who can evaluate the full picture, including your goals, labs, and history. See our medical weight loss overview for the full program. Or browse all our free health tools.

Explore Your Weight Loss Options

If your result has you considering next steps, these pages walk through the programs and medications available through Tactus Health.