Fitness and sleep calculators that show their math
Fourteen free calculators built on published formulas. Each result comes with the equation, your numbers plugged in, and the sources behind it. Nothing you type leaves your device.
All calculators
Grouped by what you want to work out. Each one shows its formula and sources.
Calories, macros and intake6 calculators
- TDEE calculatorMaintenance calories from BMR and an activity level, with all five levels side by side.
- BMR calculatorCalories at rest with Mifflin-St Jeor and Harris-Benedict, or Katch-McArdle and Cunningham from body fat %.
- Calorie calculatorMaintenance calories and what −20% to +15% works out to, with rows below BMR marked.
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- Macro calculatorCalories into grams of protein, carbs and fat, or grams back into calories and %, with a per-meal split.
- Protein calculatorGrams per day at the RDA (0.8 g/kg) and the ISSN range for people who exercise (1.4–2.0 g/kg).
- Water intake calculatorDaily total water from the EFSA and US/Canada reference values, next to per-kg rules, in liters, cups or fl oz.
Body measurements3 calculators
- BMI calculatorBody mass index with the WHO adult classes, the BMI 18.5–24.9 weight range, BMI Prime and ponderal index.
- Waist-to-height ratio calculatorWaist divided by height, with the NICE adult classes: healthy, increased or high central adiposity.
- Body fat calculatorBody fat percentage from a tape measure (U.S. Navy method), compared with the BMI-based Deurenberg formula.
Training and sleep5 calculators
- Sleep calculatorBedtimes, wake-up times, hours slept and nap alarms in sleep cycles, with an editable time to fall asleep.
- Running pace calculatorPace, time or distance in km or miles, treadmill speed to pace, splits and race-time estimates.
- Heart rate zone calculatorFive training zones with Zone 2 up front, by heart-rate reserve or % of max; Tanaka, 220 − age or Gulati.
Why every result shows its math
Most fitness calculators give you a number and nothing else. You can't see which equation produced it, which inputs mattered, or how far to trust it. Here every result opens up: the formula, your own numbers in it, the step-by-step working and the papers or official pages it comes from, each with the date it was last checked.
The formulas are tested in code against the worked examples printed on each page, so the page and the calculator can't drift apart. How the calculations are made and tested.
What this site doesn't do
- No advice, diet plans or diagnoses. The calculators show what a published formula gives for the numbers you type. What to do with that is between you and, where it matters, a doctor or dietitian.
- Not for pregnancy, children or medical conditions. The formulas were developed in healthy adults. They aren't made for those cases, and the pages say so.
- No accounts and no tracking of your numbers. Inputs stay in the page. If you tick "Remember my details on this device", they stay in this browser only.
Educational calculators based on published formulas. Not medical advice, diagnosis or treatment, and not made for pregnancy, children or medical conditions. Health disclaimer · Terms of use.