BMI Calculator

BMI places you in a band rather than giving a precise measure of health. The World Health Organization's general thresholds are below 18.5 for underweight, 18.5 to 24.9 for normal weight, 25 to 29.9 for overweight, and 30 or above for obesity.

These bands were derived from population studies showing how health risk tends to rise at the extremes. They describe statistical patterns across large groups, not predictions about any individual. Plenty of people sit outside the normal band in excellent health, and plenty inside it are not.

A single reading is also less informative than a trend. Weight fluctuates with hydration, meals and time of day, so a figure taken under consistent conditions over months tells you far more than one taken once.

The standard cut-offs were established largely from European populations, and research has since shown they understate risk for people of South Asian, Chinese and other Asian descent, who tend to carry more body fat and more visceral fat at the same BMI.

For this reason the WHO proposed lower action points for Asian populations, and Indian guidance commonly treats around 23 as the threshold for overweight and around 25 for obesity, rather than 25 and 30.

If you are of South Asian descent, a BMI of 24 sits inside the normal band by the general scale but would already be flagged under those adjusted thresholds. This calculator reports the standard WHO bands, so interpret a borderline result with that in mind and discuss it with a doctor.

BMI uses only height and weight, so it cannot distinguish muscle from fat. Well-trained athletes are frequently classified as overweight or obese despite low body fat, because muscle is denser than fat.

It equally misses the opposite case. Older adults who have lost muscle mass can show a normal BMI while carrying an unhealthy proportion of body fat, a pattern sometimes described as normal-weight obesity.

Where fat sits matters clinically as much as how much there is. Fat around the abdomen carries higher metabolic risk than fat on the hips and thighs, which is why waist circumference and waist-to-height ratio are often used alongside BMI. A waist measurement under half your height is a common rule of thumb.