What is BMI?
Body Mass Index (BMI) is a measure of body weight relative to height. It is calculated by dividing weight in kilograms by height in metres squared (kg/m²). While widely used as a screening tool, BMI has significant limitations — it does not distinguish between fat and muscle, and does not account for where fat is distributed in the body.
NHS BMI Categories
| Category | BMI Range |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5–24.9 |
| Overweight | 25–29.9 |
| Obese | 30 or above |
⚠️ The NHS uses different BMI thresholds for people of South Asian, Chinese, Black African or African-Caribbean family background, as these groups may be at higher risk at lower BMI levels. Speak to your GP for personalised advice.