BMI: A 200-Year-Old Formula That Developers Keep Getting Wrong

Adolphe Quetelet was a Belgian astronomer and mathematician, not a physician. In 1832, he analyzed population data and noticed that body weight scaled roughly with the square of height. He proposed a simple index: weight divided by height squared. Nearly two centuries later, this formula -- now called the Body Mass Index -- is used by every doctor's office, insurance company, and fitness app on the planet. As a developer who builds health tools, I find BMI fascinating not because it is a good measure of individual health (it has serious limitations) but because it is an excellent case study in how a simple formula gets adopted, misused, and defended all at the same time. The Formula BMI in metric units is straightforward: BMI = weight (kg) / height (m)^2 For a person who weighs 75 kg and is 1.75 m tall: BMI = 75 / (1.75)^2 BMI = 75 / 3.0625 BMI = 24.5 The implementation is trivially simple: def calculate_bmi(weight_kg, height_m): if height_m <= 0: raise ValueError("Height must be po