BMI Calculator

A nineteenth-century population statistic

The formula behind BMI was devised in the 1830s by the Belgian mathematician Adolphe Quetelet, who was not a doctor and had no interest in individual health. He was studying the statistical properties of populations and wanted a simple way to describe how weight scales with height across a large group. It was only in the 1970s that the measure was rebranded as the body mass index and pressed into service as a clinical screening tool, largely because it is cheap, quick, and requires nothing but a scale and a tape measure. That history explains its character precisely. It is genuinely useful for comparing groups and tracking trends across a whole society, and it was never designed to tell an individual person anything reliable about their own body.

What BMI cannot see

The formula has just two inputs, so everything else is invisible to it. It cannot distinguish muscle from fat, which is why fit, muscular people are routinely misclassified as overweight. It cannot see where fat is distributed, and yet visceral fat around the organs carries a substantially higher health risk than the same amount of fat on the hips and thighs. It takes no account of age, of sex, or of the fact that healthy body composition varies meaningfully across ethnic groups — the risk thresholds for South Asian populations, for instance, are lower than the standard ones. And it says nothing at all about fitness, diet, blood pressure or blood sugar, all of which predict health outcomes better than weight alone. A waist measurement takes ten seconds and tells you more.

This is an estimate, not medical advice

A calculator works from a formula and a handful of numbers, and a formula cannot examine you. The results here are population-level estimates derived from studies of large groups, and any individual can sit far from the average for entirely healthy reasons. They are a useful starting point for a conversation and a reasonable way to track a trend over time, but they are not a diagnosis and they cannot account for your medical history, medication, body composition or anything else a clinician would consider. If a result concerns you, or if you are making a decision about your health, speak to a doctor rather than to a web page.