Health Calculators

Every formula here is published and citable — Mifflin-St Jeor for metabolic rate, the US Navy circumference method for body fat, the WHO cut-offs for BMI. Each article names the formula, states its accuracy, and says plainly where it stops being appropriate.

That last part matters more than the numbers. BMI cannot tell muscle from fat and was never designed for individual assessment. Body fat from tape measurements is accurate to about three or four percentage points, not one. Water intake has no clinical consensus formula at all, and the eight-glasses rule has no real evidence behind it.

None of this is medical advice, and none of it accounts for your history, medication or circumstances. Treat a result as a starting point for a conversation with a doctor, not as a conclusion — and if a figure conflicts with clinical guidance you have been given, the guidance wins.