BMI Calculator (NHS)

For adults of White European background the NHS classes a BMI of 18.5 to 24.9 as a "healthy weight". For adults of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, NICE PH46 and NG246 recommend a lower healthy range of 18.5 to 22.9 — because cardiometabolic risk rises at lower BMI in these populations. The NHS uses "healthy weight" rather than "normal weight" as a deliberate public-health wording choice.

Standard 25 / 30 thresholds underestimate cardiometabolic risk in South Asian, Chinese, other Asian, Black African and African-Caribbean adults. NICE recommends lower cut-offs — overweight at BMI 23, obese at BMI 27.5 — because diabetes and cardiovascular risk rises at a lower BMI. This calculator applies the adjusted thresholds when you select the high-risk ethnicity option above.

For the general population the NHS classes a BMI of 30 or above as obese. For adults from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds the NICE-adjusted threshold is 27.5 or above. The NHS rolls obesity into a single "Obese" bucket for public-facing tools and signposts to a GP for further triage rather than splitting class I, II and III as the WHO does.

Convert your weight to total pounds (stones x 14 + pounds) then apply BMI = (total pounds x 703) / (height in inches)^2. Or convert to kilogrammes (1 lb = 0.4536 kg) and use BMI = kg / m^2. The 703 multiplier exists purely to make the imperial numerator match the metric scale of kg/m^2.

No. BMI does not distinguish lean muscle from body fat, so very muscular individuals frequently land in the overweight or obese band despite low body-fat percentage. The NHS recommends pairing BMI with waist circumference (>=94 cm in men, >=80 cm in women indicates increased risk) or a body-composition assessment when BMI alone is misleading.

Children's BMI is interpreted as a percentile against UK90 / RCPCH growth charts, not the adult thresholds. The NHS classes the 5th to 91st centile as healthy weight for ages 2-17. Use the NHS children's BMI calculator rather than this adult tool — applying the adult 18.5 / 25 / 30 cut-offs to a child is materially misleading.

No. BMI is not validated during pregnancy or in the first six months post-partum, when fluid retention, breastfeeding and recovering body composition all distort the measurement. Speak to your midwife, GP or health visitor about a healthy weight trajectory rather than relying on a BMI value during this period.

A BMI of 40 or above is classed by the NHS as severely obese and is associated with substantially elevated risk of type 2 diabetes, cardiovascular disease and certain cancers. A BMI under 16 (severely underweight) carries comparable mortality risk and warrants medical assessment. Either extreme should be discussed with your GP.

BMI captures total weight relative to height. Waist-to-height ratio (WHtR) captures central adiposity — fat around the abdomen — which is more closely linked to cardiometabolic risk. NICE NG246 recommends measuring WHtR alongside BMI in adults whose BMI is below 35; a WHtR of 0.5 or above indicates increased risk regardless of BMI band.

The NHS Better Health website offers a free 12-week weight-loss plan with personalised guidance. Your GP can also refer you to the NHS Digital Weight Management Programme if you have diabetes, hypertension or both. Sustained loss of 5-10 percent of body weight produces clinically meaningful benefits across blood pressure, blood glucose and joint pain.