BMI Calculator
Body Mass Index from your height and weight, with the WHO category.
Health information notice
This tool gives a general estimate only. It is not a diagnosis, a medical device or a substitute for professional advice. Simple formulas cannot account for your individual circumstances — the assumptions and limitations listed below describe the groups this model is not suitable for.
If the result concerns you, or you are making any health decision based on it, speak to a GP, midwife, pharmacist or other qualified health professional. The health figures you enter are used only to calculate your result and are not intentionally retained — see our privacy policy.
About this calculator
Body Mass Index is the standard first-pass screening measure relating weight to height. It won't tell you body composition, but it places you against the WHO reference ranges used by health services, and this calculator adds something more useful than the score alone: the healthy weight range for your specific height.
The formula
Worked example
78kg at 1.75m: BMI = 78 ÷ 3.0625 = 25.5 — just into the overweight band; the healthy range for that height is 56.7–76.3kg.
Common mistakes
- Treating BMI as a body-fat measure — muscular people score high with low fat.
- Applying adult thresholds to children, who use age-adjusted centile charts.
- Chasing a single number rather than the wide healthy range.
Frequently asked questions
Assumptions & limitations
Adult WHO thresholds; not valid for children, pregnancy, or frail elderly adults.
Sources & verification
- NHS — calculate your body mass index (BMI) — NHS BMI guidance and category thresholds
- WHO — obesity and overweight fact sheet — World Health Organization BMI classification
All sources last accessed 24 July 2026.
Spotted an error or an out-of-date figure? Report it — corrections are prioritised over all other work (see our corrections policy).