Health Calculators

Health numbers are only useful if you trust the math behind them. Every calculator in this collection uses published, peer-reviewed formulas — the Mifflin-St Jeor equation for metabolic rate, the US Navy circumference method for body fat, Naegele's rule for due dates — and shows the formula it used, so you can check the work or ask your clinician about it.

Start with the BMI calculator for the classic weight-to-height screen, then go deeper: body fat percentage separates fat from muscle where BMI cannot, the TDEE calculator turns your stats and activity into a daily calorie target for losing, maintaining or gaining weight, and the BMR calculator shows what you burn at complete rest. The ideal weight calculator compares the classic Robinson, Miller and Devine formulas with a BMI-based healthy range, and the water intake calculator replaces the "8 glasses" myth with a weight-based hydration target.

For family planning, the pregnancy due date calculator estimates your due date, conception date and trimester timeline from your last period, while the ovulation calculator maps your fertile window and predicts ovulation day from your cycle length.

A note that matters: these are screening and planning tools, not medical advice. If a result surprises you — especially around pregnancy, weight or body composition — take it to a qualified clinician who knows your history.