Categories
BMI categories for adults
The same four categories are used by the World Health Organization (WHO) and the US Centers for Disease Control and Prevention (CDC), for adults aged 20 and over, men and women alike.
| Category | BMI |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5 to 24.9 |
| Overweight | 25 to 29.9 |
| Obesity | 30 or more |
| Class 1 obesity | 30 to 34.9 |
| Class 2 obesity | 35 to 39.9 |
| Class 3 obesity | 40 or more |
BMI is rounded to one decimal before it is placed in a category, so 24.96 shows as 25.0 and counts as overweight. This is how the CDC calculator works too.
BMI is a screening measure
A BMI category says how your weight compares with your height, nothing more. It does not tell muscle from fat, does not show where fat is stored, and does not diagnose any condition. The CDC describes it as one possible health indicator to be considered with other factors.
Children and teens (2 to 19)
For children and teens, BMI is calculated the same way, but it is compared with other children of the same age and sex on growth charts. The result is a BMI-for-age percentile, not one of the adult categories above. Our calculator shows the BMI number for under-20s but does not guess a percentile. Use the CDC growth charts or the CDC Child and Teen BMI Calculator.
Other things worth knowing
- Waist size adds information. Fat around the middle carries more risk than the same weight elsewhere. A common guideline is to keep your waist below half your height.
- Some groups use lower action points. A WHO expert consultation (2004) noted that many Asian populations have higher health risks at lower BMI values.
- Older adults, athletes and pregnancy are situations where BMI is especially limited.
Sources
- CDC: Adult BMI categories.
- WHO: Obesity and overweight fact sheet.
- CDC: Growth charts.
- WHO Expert Consultation (2004). Appropriate body-mass index for Asian populations. The Lancet 363: 157–163.
BMI is a screening estimate, not a diagnosis and not medical advice. It does not measure body fat directly. For health questions, talk to a doctor or nurse.