Understand Your BMI: What the Number Means (and What It Doesn't)

BMI is the most-cited number in health conversations and one of the most misunderstood. It is a screening tool invented for populations, not a diagnosis for individuals. Understanding both sides makes it genuinely useful.

What BMI measures

BMI is simply weight (kg) divided by height (m) squared. It correlates with body fat across populations, which is why doctors use it as a first-pass screening indicator. The categories follow the WHO's international cut-offs.

Where the number lies

BMI cannot distinguish muscle from fat, so it misreads two big groups: athletes with high muscle mass (BMI says overweight while they are exceptionally lean) and older adults with low muscle mass (BMI says healthy while they carry high body fat). It also ignores where fat sits — abdominal fat carries higher risk than fat elsewhere, and BMI cannot see the difference.

How to use it honestly

• Treat BMI as one data point, not a verdict.
• Watch trends over time rather than single readings.
• Combine with waist measurement for a fuller picture.
• Discuss anything outside the healthy band with a clinician.