BMI calculator
Weight, height and a useful reference point. Add your waist measurement for additional context.
Understand your starting point.
Calculate your BMI and, optionally, your waist-to-height ratio. An initial guide, not a label.
A number. Some context.
Enter your details to see the category, colour and how to interpret the reference.
Age 18 or overData does not leave this calculator or get added to your contact messages.
Read about sources and tool limitationsBMI does not distinguish fat from muscle. General thresholds may not reflect risk equally in every population.
How BMI is classified
Criteria: NHS, CDC and NICE NG246. General adult classification; colours are a design choice.
Category is calculated using the full value before rounding.
The waist-to-height classification is an additional guide for adults with BMI below 35.
From age 65, BMI requires specific interpretation. We do not display a weight interval as a goal: health, muscle and functional ability should be assessed.
| Interval (kg/m²) | Category |
|---|---|
| < 18.5 | Underweight |
| 18.5 ≤ BMI < 25 | Normal weight · general reference |
| 25 ≤ BMI < 30 | Overweight |
| 30 ≤ BMI < 35 | Class I obesity |
| 35 ≤ BMI < 40 | Class II obesity |
| BMI ≥ 40 | Class III obesity |
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