BMI ranges used in UK guidance
- Below 18.5 — underweight
- 18.5 to 24.9 — healthy weight
- 25 to 29.9 — overweight
- 30 to 39.9 — obese
- 40 or above — severely obese
This is an independent calculator and is not affiliated with the NHS, but it uses these published ranges.
Waist-to-height ratio
UK guidance recommends measuring waist as well as BMI for adults with a BMI under 35. Keep your waist to less than half your height: a ratio of 0.5 to 0.59 means increased risk, and 0.6 or more high risk. At 5 ft 6 in (168 cm), half your height is 84 cm (33 in).
Where BMI falls short
BMI was designed to describe populations, not to diagnose individuals. It cannot tell muscle from fat, does not show whether fat sits around the organs or under the skin, and was built mainly on data from adults of European descent. It can underestimate risk for people of Asian background and for older adults who have lost muscle, and overestimate it for athletes. Doctors therefore combine BMI with waist size, blood pressure, blood sugar and cholesterol before drawing conclusions.
NHS Health Check and BMI
Adults in England aged 40 to 74 without certain existing conditions are invited for a free NHS Health Check every five years. It records BMI, waist, blood pressure and cholesterol and gives an estimate of heart and stroke risk. Checking your BMI beforehand with an independent tool like this one helps you know what to expect.