HEALTH TOOLS
BMI Calculator UK
Calculate your Body Mass Index using the WHO 2000 classification, the standard used by NHS England. Supports metric and imperial units.
WHO BMI Categories
| BMI Range | Classification | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Nutritional deficiency, immune suppression |
| 18.5 to 24.9 | Healthy Weight | Lowest risk in this range |
| 25.0 to 29.9 | Overweight | Moderately increased risk |
| 30.0 to 34.9 | Obese (Class I) | High risk of type 2 diabetes and cardiovascular disease |
| 35.0 to 39.9 | Obese (Class II) | Very high risk |
| 40.0 and above | Severe Obesity (Class III) | Extremely high risk |
WHO (2000). Obesity: Preventing and Managing the Global Epidemic. Used by NHS England and referenced in NICE clinical guideline CG189.
This calculator is designed for adults aged 18 to 65. It is not suitable for children, pregnant women, or people under 18 (NHS uses age-specific centile charts for children). South Asian, Chinese, and Black African populations may have lower BMI thresholds for health risk. If your BMI is below 16 or above 40, speak to your GP or contact NHS 111.
Frequently Asked Questions
What is a healthy BMI for adults in the UK?
A healthy BMI for adults is between 18.5 and 24.9 according to the WHO classification used by NHS England. However, BMI thresholds may be lower for South Asian, Chinese, and Black African populations. NICE recommends using 23 as the overweight threshold for these groups.
Is BMI an accurate measure of health?
BMI is a screening tool, not a diagnostic measure. It does not distinguish between muscle mass and fat mass, so it may overestimate body fat in athletes and underestimate it in older adults. Healthcare professionals use BMI alongside waist circumference, blood tests, and clinical history.
Can I use this BMI calculator if I am under 18?
No. BMI interpretation for children and teenagers uses age-specific and sex-specific centile charts, not the adult WHO categories. The NHS provides separate growth charts for under-18s through your GP or school nurse.
What should I do if my BMI is over 30?
A BMI over 30 is classified as obese under WHO guidelines. NICE clinical guideline CG189 recommends discussing weight management with your GP. Evidence shows that losing 5 to 10 percent of body weight significantly reduces the risk of type 2 diabetes and cardiovascular disease.
Does this tool store my data?
No. All calculations run entirely in your browser using JavaScript. No personal data is sent to any server, stored in any database, or shared with any third party.
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