BMI calculator
Work out your BMI with the NHS categories, the healthy-weight range for your height, and your waist-to-height ratio — the three quick checks worth doing before you think about weight-loss treatment.
Updated 2 November 2026
Enter your weight and height to see your BMI.
General information for adults, not a diagnosis. BMI and waist ratio don’t capture everything (muscle, body shape, pregnancy), and the NHS uses lower thresholds for some ethnic backgrounds. Talk to a GP about your own health.
What your BMI means
For adults, the NHS groups BMI like this:
- Under 18.5
- Underweight
- 18.5 to 24.9
- Healthy weight
- 25 to 29.9
- Overweight
- 30 to 34.9
- Obese (class 1)
- 35 to 39.9
- Obese (class 2)
- 40 or over
- Severely obese (class 3)
If your background is South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean, the NHS treats you as overweight from a BMI of 23 and obese from 27.5, because health risks start at a lower BMI.
Thinking about treatment?
BMI is only the start. See whether an NHS route might apply with the NHS weight-loss injection checker, work out your daily calories with the TDEE & calorie-deficit calculator, and if you do go private, always check the clinic or pharmacy is registered first.
Common questions
- How is BMI calculated?
- BMI is your weight in kilograms divided by your height in metres squared. This calculator does the maths from stone and feet or kg and cm, and shows the NHS adult category (under 18.5 underweight, 18.5 to 24.9 healthy, 25 to 29.9 overweight, 30 and over obese).
- What is a healthy BMI for my height?
- A healthy weight is a BMI of 18.5 to 24.9. The calculator turns that into a weight range in kg for your height, so you can see the healthy band rather than a single number.
- Is BMI accurate?
- BMI is a useful screen but not a diagnosis. It doesn't separate muscle from fat, so very muscular people can read high, and it doesn't apply in pregnancy or to children. The NHS also uses lower thresholds (overweight from 23, obese from 27.5) for people from South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean backgrounds. Waist-to-height ratio adds a check BMI can miss.
- What is waist-to-height ratio, and why does it matter?
- It's your waist measurement divided by your height. NICE advises keeping your waist to less than half your height (a ratio under 0.5). It flags fat carried around the middle, which carries more health risk and which BMI alone can miss. It's intended for adults with a BMI under 35.
- Does my BMI mean I can get weight-loss injections?
- BMI is one of the criteria the NHS and private providers use, but it isn't the only one, and the thresholds differ by route and nation. Use the NHS weight-loss injection checker to see which route might apply to you, and only ever through a registered clinic or pharmacy.
Categories from the NHS BMI guidance; waist-to-height from NICE.