Health & Fitness Calculators
21 free health & fitness calculators, each explaining its formula.
Body composition, energy requirements, training zones and the everyday health numbers people actually look up — with the limits of each formula stated plainly.
BMI Calculator
Enter your height and weight to get your body mass index, the WHO category it sits in, and the weight range that would put you in …
Health & FitnessBMR Calculator
Your BMR is the energy your body spends just staying alive: breathing, circulating blood, maintaining temperature and repairing ce…
Health & FitnessTDEE Calculator
TDEE is your maintenance level: eat that many calories and your weight holds steady. Everything else in nutrition planning is meas…
Health & FitnessBody Fat Percentage Calculator
No scales or scanners needed — the US Navy method estimates body fat from neck, waist and (for women) hip circumferences, which is…
Health & FitnessIdeal Weight Calculator
There is no single ideal weight, and the four formulas below will give you four different answers. That disagreement is the most u…
Health & FitnessLean Body Mass Calculator
Lean body mass is everything that is not fat: muscle, bone, organs, water and connective tissue. It is what you want to keep while…
Health & FitnessCalorie Deficit Calculator
Tell the calculator where you are, where you want to be and how long you want to take. It works out the daily deficit required — a…
Health & FitnessMacro Calculator
Calories decide whether you gain or lose. Macros decide what you gain or lose, how well you train, and how manageable the whole th…
Health & FitnessProtein Intake Calculator
The official minimum stops you becoming deficient. The optimum for someone who trains is roughly double it.…
Health & FitnessWater Intake Calculator
Fluid needs scale with body size, how much you sweat and how hot it is — not with a fixed number of glasses that someone invented …
Health & FitnessTarget Heart Rate Calculator
Percent-of-maximum zones are a rough guide. The Karvonen method, which factors in your resting heart rate, gives you zones that re…
Health & FitnessMaximum Heart Rate Calculator
Almost every heart rate zone you have ever been given rests on this one estimate — and the version most people use was never based…
Health & FitnessVO2 Max Calculator
VO₂ max is the ceiling on how much oxygen your body can use — the single best laboratory measure of aerobic fitness, and one of th…
Health & FitnessCalories Burned Calculator
MET values come from the Compendium of Physical Activities, a research catalogue of the measured energy cost of hundreds of activi…
Health & FitnessOne Rep Max Calculator
Testing a true one-rep max is risky and takes a full session. Estimating it from a set of five is safer, almost as accurate, and s…
Health & FitnessPregnancy Due Date Calculator
A due date is the midpoint of a range, not a deadline. Fewer than one baby in twenty arrives on it.…
Health & FitnessWaist to Height Ratio Calculator
One tape measurement, one division, and a threshold you can remember: keep your waist under half your height.…
Health & FitnessWaist to Hip Ratio Calculator
The ratio between your waist and your hips describes where your body stores fat — and that pattern carries independent health info…
Health & FitnessRunning Pace Calculator
Enter any two of distance, time and pace, and get the third — plus the splits you would need to hit for every standard race distan…
Health & FitnessBlood Alcohol Content Calculator
An estimate only. Individual variation is large enough that no calculator can tell you whether you are safe or legal to drive.…
Health & FitnessSleep Cycle Calculator
Waking mid-cycle is why eight hours can leave you groggy and six and a half can feel fine.…
About this section
The numbers in this section come from published research, and every one of them is an estimate built on population averages. That is worth stating plainly, because health calculators are frequently presented with a confidence they do not deserve.
A body mass index is a ratio devised in the 1830s to describe populations. A basal metabolic rate is a regression equation fitted to measured subjects, accurate to within roughly ten per cent for most people and occasionally much worse. A maximum heart rate estimate carries a standard deviation of over ten beats per minute. None of these is wrong; all of them describe a typical person rather than you specifically.
What makes them useful is that they give you a starting hypothesis to test. A calculated energy requirement is a figure to eat at for three weeks while watching what the scale actually does. A heart rate zone is a target to compare against how an effort genuinely feels. Used that way, the estimate gets corrected by reality and becomes informative. Used as a verdict, it produces false precision and sometimes real anxiety.
Each page below states the formula it applies, works through an example you can check by hand, and says explicitly where the model breaks down — who it does not apply to, and what it cannot see. The health pages in particular carry a consistent caution: nothing here diagnoses anything, and none of it replaces a conversation with a clinician who can examine you.