Guides
Is BMI accurate?
BMI is useful for groups and limited for individuals.
Short answer
BMI is a reasonable screening tool across large populations, but for one person it can be misleading, because it uses only height and weight. It cannot separate muscle from fat, show where fat is stored, or account for age, sex and ethnicity.
What BMI cannot see
- Muscle versus fat: a very muscular person can have a high BMI and little body fat.
- Where fat is carried: fat around the waist carries more health risk than the same fat elsewhere, and BMI does not show it.
- Age: older adults tend to lose muscle and may have more body fat at the same BMI.
- Ethnicity: risk can start at lower BMI values in some populations.
- Pregnancy and some medical conditions change weight in ways BMI does not account for.
What else is used
- Waist circumference or waist-to-height ratio, where a ratio under 0.5 is a commonly cited rule of thumb.
- Body composition measurements.
- Blood pressure, blood sugar, cholesterol and family history.
- Fitness, diet and daily activity.
How to use your result
Treat BMI as one reference point, not as a verdict. If your result worries you, or if you are making changes to your weight, speak to a doctor or another health professional. See the category chart for the ranges.
Frequently asked questions
Why do athletes often have a high BMI?
Muscle is dense, so a very muscular person can weigh more than their height suggests without carrying excess fat. BMI cannot tell the difference.