What is a healthy BMI for adults in the UK?

For adults, a healthy BMI is between 18.5 and 24.9. Below 18.5 is considered underweight, 25–29.9 is overweight, and 30 or above is obese. For South Asian, East Asian, and Black African populations, NICE recommends lower intervention thresholds of 23 (increased risk) and 27.5 (high risk).

Is BMI an accurate measure of health?

BMI has limitations — it does not distinguish between muscle and fat, nor does it measure where fat is stored. Waist-to-height ratio is considered a better predictor of metabolic risk by many researchers. A BMI result should be considered alongside waist circumference, blood pressure, and other health markers.

How is BMI calculated?

BMI is calculated by dividing your weight in kilograms by your height in metres squared (kg/m²). For example, a person weighing 75kg who is 1.75m tall has a BMI of 75 ÷ (1.75 × 1.75) = 24.5.

Health & Fitness

BMI Calculator – Body Mass Index, Waist Ratio & Healthy Weight Range

The most complete free UK BMI calculator. Calculates your BMI, waist-to-height ratio (a more accurate measure of metabolic risk), your healthy weight range, ideal weight, and ethnicity-adjusted thresholds — plus children's BMI centile for ages 2–18.

Based on WHO, NHS & NICE guidelines · Adult and children's calculations

✅ Rates verified April 2026 · Sourced from HMRC, DWP & UK legislation · About our verification process

BMI Categories for Adults

UnderweightBelow 18.5

Healthy weight18.5 – 24.9

Overweight25.0 – 29.9

Obese30.0 and above

Why BMI Alone Is Not Enough

BMI is a useful population-level screening tool, but it has well-documented limitations. It does not distinguish between fat and muscle — a very muscular person may have a high BMI but low body fat. It does not account for where fat is stored — abdominal fat (around the waist) carries significantly more metabolic risk than fat stored elsewhere. And it uses the same thresholds for all ethnic groups, despite evidence that health risks increase at lower BMI levels for South Asian, East Asian, and Black African populations.

For this reason, this calculator also provides your waist-to-height ratio (WHtR), which is considered by many researchers to be a better predictor of cardiovascular disease, type 2 diabetes, and metabolic syndrome than BMI alone. A WHtR below 0.5 is generally considered healthy for all adults.

Ethnicity-Adjusted BMI Thresholds

NICE guidelines recommend lower intervention thresholds for people from South Asian, Chinese, other Asian, Middle Eastern, Black African, and African-Caribbean backgrounds, because these groups carry higher cardiometabolic risk at a lower BMI than the general white European population.

Ethnic group	Increased risk BMI	High risk BMI
White European (standard thresholds)	25.0	30.0
South Asian, Chinese, other Asian, Middle Eastern	23.0	27.5
Black African / African-Caribbean	23.0	27.5

Waist-to-Height Ratio (WHtR)

Your WHtR is calculated by dividing your waist circumference by your height (both in the same unit). A ratio below 0.5 is considered healthy for most adults. Between 0.5 and 0.6 indicates increased risk; above 0.6 indicates high risk. The simple rule of thumb is: keep your waist less than half your height.

Waist circumference alone is also used clinically: above 94cm (37in) for men or 80cm (31.5in) for women indicates increased health risk; above 102cm (40in) for men or 88cm (34.5in) for women indicates high risk.

Children's BMI: BMI thresholds for children and teenagers are completely different from adult thresholds. Children's BMI is expressed as a centile — their BMI relative to other children of the same age and sex. The calculator provides a centile estimate for ages 2–18 using UK90 growth reference data.

BMI limitations: BMI is a screening tool, not a diagnosis. A single number cannot fully represent your health. Always discuss your weight and health with your GP, who can consider your full clinical picture including blood pressure, cholesterol, blood sugar, family history, and lifestyle factors.