BMI Categories (NHS)
| BMI Range | Category |
|---|---|
| Under 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25 – 29.9 | Overweight |
| 30 – 34.9 | Obese Class I |
| 35 – 39.9 | Obese Class II |
| 40 and over | Obese Class III (morbidly obese) |
This calculator is for adults (18+) only. BMI is a screening tool, not a diagnostic measure. Always consult a healthcare professional for health advice.
Limitations of BMI
- Does not distinguish fat from muscle — athletes may have a high BMI without excess fat.
- Does not account for fat distribution — abdominal fat is more health-significant than other fat.
- Different thresholds apply to South Asian adults: ≥23 is overweight, ≥27.5 is obese.
- Not valid for children (under 18), pregnant women, or people over 85.
How is BMI calculated?
BMI = weight (kg) ÷ height (m)². E.g. 70kg ÷ (1.75m)² = 22.9. In imperial: (weight in lbs × 703) ÷ (height in inches)².
What is a healthy BMI for adults in the UK?
The NHS defines 18.5–24.9 as healthy weight for adults. Under 18.5 is underweight; 25–29.9 is overweight; 30+ is obese.