Health & Fitness Calculators

Health calculations are useful as reference points rather than verdicts. BMI, body fat estimates, calorie targets and heart rate zones are all population-level formulas: they describe averages well and individuals only approximately. Every tool here shows the formula it uses and the assumptions behind it, so you can judge how well it applies to you rather than taking a single number at face value.

BMI is the clearest example. It divides weight by height squared, which means it does not distinguish muscle from fat and systematically misreads very muscular or very tall people. It remains widely used because it is cheap to compute and correlates well across large populations, not because it is precise for one person. Waist measurement and waist-to-height ratio add useful information that BMI alone misses.

Where a formula has competing versions, the calculator says which one it uses. Basal metabolic rate can be estimated by Mifflin-St Jeor or Harris-Benedict and they disagree by a hundred calories or more; maximum heart rate has several formulas that differ by several beats per minute. None of these tools give medical advice, and none of them replace a clinician who can see the whole picture — treat them as a starting point for a better question.