Health calculators
Quick, private calculators for weight, calories, water, pregnancy, fertility and sleep, using the formulas doctors and dietitians rely on. General information only, not medical advice.
The tools
See every ZapKit toolBody
2 toolsBMI with Indian and WHO categories, and body fat by tape measure.
Daily needs
4 toolsCalories at rest and in a day, water to drink, and when to sleep.
- BMR calculatorCalories your body burns at rest, by Mifflin–St Jeor and other formulas.
- TDEE calculatorDaily calories you burn, and targets to lose, keep or gain weight.
- Water intake calculatorHow much water to drink a day for your weight, exercise and climate.
- Sleep calculatorBedtimes and wake-up times that line up with 90-minute sleep cycles.
Pregnancy & cycle
2 toolsDue date and weeks pregnant, fertile days and ovulation.
Frequently asked questions
Are these calculators medical advice?
No. They use well-known formulas that work for average adults, but can't account for your health history. Speak to a doctor or dietitian before acting on a result.
Is my health information stored?
No. Everything is calculated in your browser. Your inputs are only in the page link, which nobody sees unless you share it.
Why does the BMI calculator use different categories for Indians?
Research shows South Asians face higher health risks at lower BMIs, so Indian and WHO Asia-Pacific guidance uses 23 and 25 as the overweight and obesity cut-offs. You can switch to the international scale.
Can I use metric and imperial units?
Yes. The body calculators accept centimetres and kilograms, or feet, inches and pounds.