Understanding BMI: what the number means and where it falls short
Body Mass Index (BMI) is calculated by dividing your weight in kilograms by the square of your height in metres (kg/m²). The World Health Organization classifies adults into four categories: underweight (below 18.5), normal weight (18.5–24.9), overweight (25–29.9), and obese (30 and above). It is the most widely used population-level screening tool for healthy weight because it requires no equipment and can be calculated in seconds.
BMI is a useful starting point, but it has real limitations at the individual level. It cannot distinguish between muscle and fat — a highly muscular person can show an “overweight” BMI while carrying very little body fat. It also cannot detect where fat is distributed: visceral fat around the abdomen carries significantly higher cardiometabolic risk than subcutaneous fat elsewhere. Age, sex, and ethnicity all affect the relationship between BMI and actual health outcomes.
The articles below pair BMI with complementary measures — body fat percentage, waist-to-height ratio, and age-specific context — to give a more complete picture of what the numbers mean. All guides follow WHO guidelines and cite peer-reviewed research where specific claims are made. They were written by Dariusz Łapiński, the developer behind BMI Tracker.
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