Is BMI a scam? More than a few experts say yes BMI can "label a huge swath of our population as somehow aberrant because of their weight, even if they’re perfectly healthy." istockphoto Related Stories There are few single measures in health care that seem to carry as much weight as body mass index, or BMI. We encounter it not just at doctor’s offices, but with online calculators and smart scales, at gyms and even when determining eligibility for the COVID vaccine. Its formula is simple: Take your weight (in kilograms), and divide by the square of your height (in meters). The result, which slots you into one of four main categories, is meant to describe your body in a single word or two: underweight (BMI less than 18.5), normal weight (18.5 to 24.9), overweight (25.0 to 29.9) or obese (30 or greater).