What BMI is measuring
Body mass index compares your weight against your height. It was devised in the nineteenth century as a way of describing populations, and it remains genuinely useful for that: it is cheap, needs no equipment, and tracks well with health outcomes across large groups of people.
Applied to one individual it is a much blunter instrument, because two numbers cannot distinguish muscle from fat or tell where on the body that weight is carried. Treat it as a starting point that tells you whether a conversation is worth having, not as a verdict.
The healthy range is a range for a reason
The calculator shows the weight band that corresponds to a BMI of 18.5 to 24.9 at your height, which for most people is a span of fifteen kilograms or more. There is no single correct weight inside it. Where you sit within that band matters far less than whether you are active, what you eat, and how your weight has moved over time.
Why the thresholds shift by ethnicity
The standard cut-offs were derived largely from European populations, and they under-predict risk for South Asian, Chinese and some other groups, who tend to carry more visceral fat at the same BMI. Indian clinical guidance commonly treats 23 as the overweight threshold and 25 as obese. If you are of South Asian descent and this calculator puts you in the healthy band near its upper end, that is worth knowing.
What to measure alongside it
Waist circumference adds most of what BMI is missing, because abdominal fat is the kind most strongly linked to metabolic risk. A waist above 90cm for men or 80cm for women is the threshold used in most Indian guidance. Two cheap numbers together tell you far more than either alone.