Educational; not medical advice.
Uses the Mifflin–St Jeor style BMR with weight in kg, height in cm, age in years, and sex offset; then TDEE = BMR × activity factor. Age is clamped to a plausible band in code; results below a sanity floor are rejected. This is a population estimate, not a medical prescription.
This calculator uses plain decimal numbers. If a result looks wrong, check whether you used a comma instead of a dot (or vice versa) where the field expects one.