What your BMI means
Body mass index is your weight in kilograms divided by your height in metres squared. The World Health Organization uses these bands for adults:
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25 to 29.9 | Overweight |
| 30 and above | Obesity |
Lower cut-offs for Asian adults
People of South Asian, Chinese and other Asian backgrounds tend to develop type 2 diabetes and heart disease at a lower BMI. A WHO expert consultation published in The Lancet suggested 23 as the point where risk starts to rise and 27.5 as the point of high risk for these groups. If that’s you, treat 23 as your signal to look at waist size, blood sugar and blood pressure too.
What BMI can’t tell you
- It doesn’t separate muscle from fat, so very muscular people can score as overweight.
- It says nothing about where fat sits. Fat around the waist carries more risk than fat on the hips.
- It isn’t used the same way for children, teenagers or during pregnancy.
- Older adults can lose muscle and have a “healthy” BMI while carrying too much fat.
So read BMI as a first screen. A waist measurement, blood pressure, blood sugar and cholesterol give the fuller picture. If your number is above the healthy range, our guide to prediabetes signs and how to reverse it is a useful next read, and the calorie calculator shows what a steady deficit looks like.
When to see a doctor
- Your BMI is 30 or more, or 27.5 or more if you’re of Asian background.
- Your BMI is under 18.5, or you’ve lost weight without trying.
- You have a BMI over 25 along with high blood pressure, high blood sugar or a family history of diabetes or heart disease.
Frequently asked questions
Is BMI different for men and women?
The formula and adult categories are the same. Women usually carry more body fat than men at the same BMI, which is one reason BMI is only a rough guide.
What is a healthy BMI?
18.5 to 24.9 for most adults. For Asian adults, staying under 23 is linked with lower risk.
How do I calculate BMI by hand?
Divide your weight in kg by your height in metres, then divide by your height again. For example, 70 kg and 1.70 m gives 70 / 1.70 / 1.70 = 24.2.
These tools give general estimates for adults and are not a diagnosis or a substitute for advice from a doctor. If you have symptoms or a health condition, please consult a qualified healthcare professional.