Guide
What BMI can and cannot tell you about your health
A plain guide to what the BMI calculation measures, where it is unreliable, and why it is a starting point rather than a verdict.
BMI is a population tool, not a personal diagnosis
BMI was developed in the 19th century as a quick way to describe the weight distribution of populations, not to assess individual health. It divides weight by height squared and produces a number that epidemiologists use to study population-level patterns. Using it as a personal health verdict stretches it well beyond what the formula was designed to do.
Muscle, fat distribution, age, and ethnicity all affect its accuracy
A fit, muscular person can have a high BMI without a high body fat percentage. An older person can have a normal BMI but a high fat-to-muscle ratio. Fat concentrated around the abdomen carries different health risks than fat elsewhere. South Asian adults may face elevated risk at lower BMI thresholds than the standard WHO ranges. The number misses all of this.
Use it as context, not a conclusion
A BMI result outside the healthy range is a prompt to have a conversation with a doctor, not a diagnosis or a directive. A clinician can assess your actual health picture using blood pressure, blood tests, fat distribution, fitness level, and your medical history — information that weight and height alone cannot provide.