BMI chart: what each range means
Body Mass Index (BMI) is the fastest way to get a sense of whether your weight falls within a healthy range for your height. But the number alone says little: what matters is understanding which range it falls into and what that means in practice. This guide explains the World Health Organization (WHO) BMI chart, what each category represents, and — most importantly — the limitations you should know before drawing conclusions.
| BMI (kg/m²) | Classification |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Normal weight |
| 25.0 to 29.9 | Overweight |
| 30.0 to 34.9 | Obesity class I |
| 35.0 to 39.9 | Obesity class II |
| 40.0 or more | Obesity class III |
How to read the BMI chart
To use the chart, find your BMI in the first column and read the matching classification. For example, a BMI of 27 falls in the 25.0–29.9 range, indicating overweight. A BMI of 22 is within the normal range.
The chart applies to adults aged 18 and over. For children and teenagers, interpretation differs: BMI-for-age is used, comparing the result against reference percentiles for the same age group.
What each range means for your health
Underweight may signal nutritional deficiencies, loss of muscle mass, or a health condition that deserves attention. Normal weight is the range associated with the lowest statistical risk of weight-related diseases.
Overweight is often an early warning sign, especially when accompanied by abdominal fat. Obesity — split into three classes — is linked to a higher risk of type 2 diabetes, high blood pressure, and cardiovascular disease, with risk rising by class.
Why BMI doesn't tell the whole story
BMI is a population-level measure, designed to analyze groups rather than individuals. It does not distinguish muscle from fat: a very muscular person may have a high BMI without excess fat. Likewise, someone with a normal BMI may have a high body-fat percentage and little muscle.
The index also ignores fat distribution, which is an important risk factor. That's why measures such as waist circumference complement BMI. Age, sex, and ethnicity also affect interpretation.
What to do after calculating your BMI
Use BMI as a starting point, not a verdict. If your result is outside the normal range, look at other signals: your diet, your physical activity level, and your health history.
The safest next step is to bring the result to a doctor or dietitian, who can assess body composition, lab results, and individual context. BMI starts the conversation; a professional completes the diagnosis.
Frequently asked questions
What is a BMI of 27 considered?
A BMI of 27 falls in the 25–29.9 range, classified as overweight by the WHO.
What's the difference between overweight and obesity?
Overweight is a BMI between 25 and 29.9. Obesity starts at 30 and is divided into three classes, with rising health risk.
Does BMI work for older adults?
In older adults, BMI should be interpreted carefully, since natural loss of muscle mass can mask the result. Professional assessment is especially important in this group.