What is BMI?
BMI stands for Body Mass Index. It’s a simple number worked out from your height and weight that gives a general idea of whether your weight sits in a healthy range for your height. It’s widely used because it’s quick and needs no special equipment. For the full ranges and BMI's limitations, see our guide: What Is a Healthy BMI?
BMI categories for adults
- Under 18.5 — Underweight
- 18.5 – 24.9 — Healthy weight
- 25.0 – 29.9 — Overweight
- 30.0 and above — Obese range
What BMI does not tell you
BMI is a helpful starting point, but it’s not the whole picture. It doesn’t separate muscle from fat, so very muscular people can show a high BMI while being perfectly healthy. It also doesn’t account for age, sex differences, or where fat is stored. Treat it as one simple signal — not a diagnosis. For personal health advice, always talk to a doctor.