Tool

BMI Calculator

All calculations show inputs, formula, date and disclaimer

What BMI is, and what it is not

Body mass index is a ratio of weight to height, calculated as 703 × pounds ÷ inches². It was designed as a population-level screening measure, not an individual diagnostic, and it has been used as one ever since.

It does not measure body composition, fat distribution, fitness or health. It does not distinguish muscle from fat, which is why it misclassifies athletic builds. It performs differently across ages and ancestries, and the conventional thresholds were derived from populations that do not represent everyone they are now applied to.

Why it appears in this market at all

BMI thresholds are used in prescribing criteria and in insurance prior-authorisation rules — commonly a BMI of 30 or above, or 27 or above with a weight-related condition. That is why the number matters practically even where it describes you poorly.

Knowing your BMI tells you which criteria you may meet on paper. It does not tell you whether a medication is appropriate for you, and no calculator can. That assessment belongs with a clinician who knows your history, your bloodwork and your circumstances.

What this tool does with your numbers

Nothing. The calculation runs in your browser. Nothing is transmitted, stored or written to your device, and we never ask for health information. You can verify that in your browser's network inspector.

What this number is, and what it is not

Body mass index is weight divided by height squared. It was devised in the nineteenth century as a population statistic, not a diagnostic test, and that is still what it is best at.

It does not distinguish muscle from fat, does not account for where fat is carried, and was derived overwhelmingly from European populations. A muscular person can register as obese; someone with low muscle mass and central adiposity can register as healthy while carrying real metabolic risk.

Why prescribing criteria use it anyway

Because it is cheap, reproducible and requires no equipment beyond scales and a tape measure. Every prior-authorization criterion in this category is written around it, typically at a threshold of 30, or 27 with a weight-related comorbidity such as type 2 diabetes, hypertension or obstructive sleep apnoea.

That is why the number matters practically even where it is a poor individual measure: it is the gate your insurer applies. Our prior authorization guide covers what else the criteria usually require.

Reading your result

The bands are conventional cut-offs, not cliffs. A BMI of 29.9 and one of 30.1 describe near-identical bodies; only the paperwork differs. Waist circumference and waist-to-height ratio capture central adiposity better and are worth asking about alongside.

If your result sits just below a threshold that matters for coverage, that is a conversation with a clinician about the full picture rather than a reason to adjust how you measure.

What we do not do here

We do not tell you a target weight, a calorie figure or a rate of loss. Those depend on your history, your bloods and your medications, and a number generated from two inputs cannot know any of it.