BMI calculator

BMI is weight in kilograms over the square of height in metres, a nineteenth-century population measure that remains the standard first screen. The cutoffs are fixed: below 18.5 reads as underweight, 18.5 to 24.9 as healthy, 25 to 29.9 as overweight, and 30 or above as obese. What the number cannot do is see inside a body: it scores muscle the same as fat, it was built on European populations, and it shifts meaning at the extremes of height. Treat it as one line of context next to waist size, bloodwork, and medical advice, not as a verdict.