Why two sets of numbers?

The familiar BMI categories — healthy weight up to 25, overweight from 25, obese from 30 — were derived largely from European populations. A WHO expert consultation concluded that people of Asian descent, including South Asians, develop cardiometabolic risk such as type 2 diabetes and high blood pressure at a lower BMI than those thresholds imply.

That is why this calculator shows both. If you are of South Asian origin, the lower set is the more useful guide: risk starts rising around 23 rather than 25.

What BMI cannot tell you

BMI is a ratio of weight to height. It has no way of knowing what that weight is made of, which is why it is a screening signal rather than a verdict:

Muscle weighs more than fat, so athletes are routinely classified as overweight while carrying very little fat.
It says nothing about where fat sits. Fat around the abdomen carries more metabolic risk than fat on the hips, and BMI cannot distinguish them — our waist-to-height calculator is often more informative.
It is not valid during pregnancy, and children need age-and-sex-specific growth charts instead.
Older adults naturally lose muscle, which can make BMI look reassuring when it should not.

What to do with the number

If your BMI falls outside the healthy range, that is a reason to have a conversation, not to start a crash diet. A doctor or pharmacist can look at it alongside your waist measurement, blood pressure, blood sugar and family history — which together say far more than BMI alone ever will.

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