BMI limits: what the number misses
BMI uses only height and weight, so it cannot tell muscle from fat or show where fat sits. It is a quick screening number, and a poor judge of one person's health.
Updated 21 October 2026. Sources named on the page.
- Five things BMI cannot see
- Why athletes and older adults can read oddly
- What else professionals look at
- When to talk to a doctor
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Work out your number first
Get your BMI, then read it with these limits in mind.
Where the number comes from
BMI is only this: weight in kilograms divided by height in metres squared. Nothing else goes in, which is both why it is simple and why it is limited.
Sources: World Health Organization, adult BMI classification and expert consultation on appropriate body mass index for Asian populations
Figures and sources checked 21 October 2026. General information, not medical advice.
What BMI cannot see
BMI is a ratio of weight to height. It does not know what that weight is made of or where it sits on the body.
- Muscle versus fat: muscle is denser, so a muscular person can score high without carrying extra fat.
- Where fat sits: fat around the waist is linked with more risk than fat elsewhere, and BMI cannot tell the difference.
- Age: older adults can lose muscle and keep the same weight, so the same BMI can mean more fat.
- Background: some groups have different risk at the same BMI, and some guidelines use different cut-offs.
- Fitness and habits: how active you are, what you eat, how you sleep and your blood tests are not in the number.
Why it is still used
BMI is quick, free and the same everywhere, which makes it useful for looking at large groups. For one person it works best as a prompt to look further, not as a result.
What else gets looked at
A doctor or dietitian may also consider waist measurement, blood pressure, blood sugar, cholesterol, family history, fitness, and how you feel. These give a much fuller picture than any single number.
A kind way to use it
If your BMI is outside the usual range, treat it as a reason to ask a question, not a reason to worry. If it is inside the usual range, it does not mean there is nothing to look after. Steady habits such as movement, sleep and regular meals matter more than a decimal.
Questions
Is BMI a good measure of health?
It is a rough screening tool for groups. For one person it misses muscle, fat distribution and many health markers, so it should not be used alone.
Why can an athlete have a high BMI?
Muscle weighs more than the same volume of fat, so a very muscular person can have a high BMI without extra body fat.
Is there a better number than BMI?
No single number is best. Waist measurement and blood tests add useful information, and a doctor can advise which to use.
Should I be worried about my BMI?
One number is not a diagnosis. If you are concerned about your weight or health, speak to a doctor or an accredited practising dietitian.
Keep going
Look at habits, not only a number
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