Health & Fitness

These calculators use published equations such as Mifflin-St Jeor for resting energy and the US Navy circumference method for body fat, and each page names the equation it uses.

They give screening estimates for adults, not diagnoses. Each one lists who it does not apply to and when a clinician should be the one doing the measuring.

11 tools · updated October 19, 2026

BMI Calculator Calculate your Body Mass Index from weight and height in metric or US units, with the WHO category and the healthy weight range for your height. BMR Calculator Estimate your basal metabolic rate with the Mifflin-St Jeor equation and the calories you burn per day at five activity levels. Body Fat Calculator Estimate body fat percentage from height, waist, neck and (for women) hip measurements with the US Navy tape method, rated on the ACE chart. Ideal Weight Calculator Compare ideal body weight for your height from the Hamwi, Devine, Robinson and Miller formulas, with their average in pounds and kilograms. Calorie Deficit Calculator Estimate the daily calorie intake needed to lose a target number of pounds by a deadline, with warnings when the pace is too fast. Water Intake Calculator Estimate daily water needs from body weight plus fluid lost during exercise, compared with the National Academies adequate intake. Heart Rate Zone Calculator Calculate five training heart rate zones from age-predicted maximum heart rate (220 − age or Tanaka), optionally with the Karvonen method. Macro Calculator Split a daily calorie budget into grams of protein, carbohydrate and fat for your goal, with the protein per kilogram of body weight. Sleep Calculator Find bedtimes or wake-up times that fit whole 90-minute sleep cycles plus 15 minutes to fall asleep. Protein Needs Calculator Calculate a daily protein target in grams from body weight, activity and goal, from 0.8 to 2.0 g per kg, split across four meals. Flexibility Test Calculator Rate a sit-and-reach result in centimeters from Poor to Excellent using separate bands for men and women.

Which health number answers your question

BMI, body fat or ideal weight?

They measure different things. BMI compares weight with height and is a quick population screen that cannot tell muscle from fat. The body fat calculator estimates composition from tape measurements (the US Navy method), which is more informative for muscular people. The ideal weight calculator shows clinical reference formulas, mainly used for drug dosing; they disagree by several kilograms, and none is a personal goal.

Planning food intake, step by step

Start with resting energy from the BMR calculator (Mifflin-St Jeor), which also multiplies by an activity level to estimate daily needs. The calorie deficit calculator turns a target weight and date into a daily budget and flags plans that are too aggressive. Split that budget into protein, carbohydrate and fat with the macro calculator, or check protein alone in grams per kilogram with the protein needs calculator.

Training, recovery and hydration

The heart rate zone calculator uses the Karvonen method, which takes your resting pulse into account rather than age alone. The water intake calculator adds measured sweat loss to a baseline, and the sleep calculator lines bedtimes up with roughly 90-minute cycles, an average that varies from person to person. The flexibility test rates a sit-and-reach score and is most useful when compared with your own earlier attempts.

Who should not rely on these

All of these tools are written for healthy adults. Children and teenagers, pregnant or breastfeeding people, older adults with low muscle mass and anyone with a medical condition that affects weight, heart rate or fluid balance should get targets from a clinician. Each calculator page lists its own exclusions in the section before the FAQs.