Adult BMI Calculator
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What is BMI?
Body mass index (BMI) is a widely used screening tool for estimating body fat based on your height and weight. While it doesn’t directly measure body fat, BMI can help 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. A BMI score can suggest whether you may be at risk for certain health conditions, particularly those related to weight such as type 2 diabetes and cardiovascular disease. It can also help Glo providers determine whether you qualify for prescription weight loss treatments like compounded semaglutide or tirzepatide.
That said, 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 in, despite being key predictors of body composition and disease risk.
Even so, 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.
How to calculate BMI
Metric: BMI = weight (kg) ÷ height² (m²)
Imperial: BMI = [weight (lb) ÷ height² (in²)] × 703
BMI measurements are divided into four main categories underweight, normal, overweight, and obesity which is further broken into three classes. These classifications are based on CDC ranges and apply to adults aged 20 and older:
Underweight
< 18.5
Healthy Weight
18.5 – 24.9
Overweight
25 – 29.9
Class 1 Obesity
30 – 34.9
Class 2 Obesity
35 – 39.9
Class 3 Obesity
> 40
| Category | BMI Range | Risk Level |
|---|---|---|
| Underweight | < 18.5 | Low weight |
| Normal / Healthy | 18.5 – 24.9 | Healthy range |
| Overweight | 25 – 29.9 | Elevated risk |
| Class 1 Obesity | 30 – 34.9 | High risk |
| Class 2 Obesity | 35 – 39.9 | Very high risk |
| Class 3 Obesity | > 40 | Severe risk |
What does my BMI number mean?
- Underweight (<18.5): Can be associated with increased risks of malnutrition, weakened immune function, and osteoporosis — especially among older adults.
- Normal weight (18.5–24.9): Generally considered to carry the lowest overall risk of chronic diseases related to weight.
- Overweight (25–29.9): May be associated with elevated risk for high blood pressure, insulin resistance, and heart disease — especially with other risk factors like excess abdominal fat.
- Class 1 Obesity (30–34.9): Significantly increased risks for type 2 diabetes, cardiovascular disease, and sleep apnea.
- Class 2 Obesity (35–39.9): Greater cardiometabolic risk, often linked to reduced mobility and liver disease.
- Class 3 Obesity (>40): Highest risk for serious chronic conditions, including certain cancers.
What BMI doesn't tell you
- How much of your weight is muscle vs. fat. Someone with a high level of muscle mass may be classified as overweight even if their body fat is low and health markers are optimal.
- Where fat is stored in your body. isceral fat (concentrated in the abdomen) poses greater health risks yet two people with the same BMI can have very different fat distributions.
- Your metabolic health. Blood pressure, cholesterol, blood sugar, and inflammation levels are all critical health markers that BMI doesn't capture.
- Your fitness level or physical strength. Studies show that people with higher BMIs who are physically fit may be healthier and live longer than those with lower BMIs who are sedentary.
- Your biological age, sex, or genetics. Biological women have greater amounts of total body fat than men with equal BMIs yet sex isn't factored into the calculation.
- Your race and ethnicity. The BMI system was created from predominantly white population studies. Research suggests, for example, that Asian Americans develop obesity-related health conditions at lower BMIs than white Americans.
- Your habits and lifestyle. How you eat, sleep, and manage stress all meaningfully impact your weight and overall health none of which BMI captures.
How to use your BMI range
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 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 through Glo.
No matter your number, the most helpful next step is to speak with a licensed healthcare provider who can evaluate the full picture — your goals, lab work, family history, mental health, and more. At Glo, that starts with a free 3-minute quiz. No appointments, no waiting rooms.
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