My smartwatch told me I burned 3,400 calories yesterday. My partner's app told me I burned 2,200. Both are wrong, in different directions, and I am tired of trusting black boxes that disagree. So I sat down with the formulas a sports scientist would actually use and built a tiny CLI for myself. This post is the boring, deterministic version of fitness math. No heart rate sensors, no proprietary algorithms, just the same equations dietitians have used for decades. The TypeScript is short on purpose; the value is in seeing the formulas written next to each other. BMI: not a fitness number, but a useful baseline First, the dumbest one. BMI is a quick way to flag whether someone is in a healthy weight range, no more.…