How to Calculate Your BMI (and Why It's Not the Whole Story)

Body Mass Index is the first thing most providers check when evaluating you for GLP-1 medication. The FDA-approved thresholds are straightforward: BMI of 30 or higher, or 27 or higher with a weight-related comorbidity. But while BMI is the standard screening tool, it has well-known limitations.

How BMI Is Calculated

BMI divides your weight in kilograms by your height in meters squared. In US customary units, the formula is: weight (lbs) ÷ height (inches)² × 703. It's a fast screening tool, but it's not a direct measure of body fat, metabolic health, or disease risk.

Where BMI Falls Short

BMI doesn't distinguish between muscle mass and fat mass. A person who strength trains may have a high BMI with a healthy body composition. Conversely, someone with a "normal" BMI can carry a significant amount of visceral fat — the type stored around internal organs that drives metabolic disease.

BMI also doesn't account for fat distribution. Abdominal fat (measured by waist circumference) is more strongly associated with cardiovascular risk and insulin resistance than overall weight. Two people with the same BMI can have very different risk profiles depending on where they carry their weight.

Additionally, BMI thresholds were developed primarily from studies of white European populations. Research has shown that health risks associated with excess body fat may occur at lower BMIs in some Asian populations, and at higher BMIs in some Black populations. The standard cutoffs are a simplification.

What Else Your Doctor Should Consider

A thorough GLP-1 evaluation should go beyond a single number. Here's what a good provider will also assess:

Waist circumference — Greater than 40 inches in men or 35 inches in women is associated with increased metabolic risk, regardless of BMI
Metabolic markers — A1C, fasting glucose, lipid panel, blood pressure. These can indicate metabolic dysfunction even in someone with a borderline BMI
Weight history — Chronic weight cycling, difficulty maintaining weight loss, and duration of obesity all factor into clinical decision-making
Comorbidities — Type 2 diabetes, hypertension, dyslipidemia, sleep apnea, cardiovascular disease, PCOS, osteoarthritis, NAFLD/MASH
Previous interventions — What you've tried before (diet, exercise, other medications, behavioral programs) and the outcomes

Why BMI Still Matters for Eligibility

Despite its limitations, BMI is the metric that FDA labeling and insurance prior authorization criteria use. If you're seeking a GLP-1 prescription — whether through your PCP or a telehealth platform — your BMI will almost certainly be the first eligibility check. Knowing your number before your appointment helps you walk in prepared.

If your BMI falls just below the threshold, bring documentation of your weight-related conditions. A BMI of 28 with type 2 diabetes and hypertension is absolutely eligible — but you may need to make the case with supporting records, especially if you're seeking insurance coverage.

Bottom Line

BMI is a starting point, not a finish line. It opens the door to the conversation, but your doctor should be looking at the full clinical picture. If a provider bases their entire evaluation on a single number without asking about your metabolic health, weight history, or comorbidities, that's worth questioning.