Free tools
Health and fitness calculators
Quick answers to the numbers your Apple Watch and your training throw at you. Every page shows its published sources and the date its figures were last checked. No sign-up, and every calculator runs in your browser: nothing you type is sent anywhere.
113 free tools
Heart
Max heart rate, training zones, resting heart rate, blood pressure categories, target heart rate, calories from heart rate, METs, the six-minute walk, recovery and cardio fitness.
Resting heart rate by age
See where your resting heart rate falls among people your age and sex, using national NHANES percentiles.
OpenVO2 max by age
Compare your Apple Watch Cardio Fitness with measured treadmill VO2 max percentiles by age and sex.
OpenHeart rate recovery
Calculate your one-minute heart rate recovery and see how Apple Watch Cardio Recovery is measured.
OpenMax heart rate calculator
Your age-predicted maximum heart rate from four published formulas.
OpenHeart rate zone calculator
Light, moderate and vigorous heart rate ranges from your resting and max heart rate.
OpenVO2 max calculator
Estimate VO2 max from a 12-minute run, a one-mile walk or your heart rates.
OpenBlood pressure checker
Which ACC/AHA category a reading falls in, with pulse pressure.
OpenTarget heart rate calculator
Moderate and vigorous heart rate ranges for your age, from the AHA.
OpenHeart rate calories calculator
Calories burned from average heart rate, with the Keytel equations.
OpenSix-minute walk test calculator
Reference six-minute walk distance for healthy adults aged 40–80.
OpenMETs calculator
Convert METs, oxygen uptake and calories per minute.
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Recovery and training load
Session training load and TRIMP, how fast load is rising, reading your HRV against your own baseline, and a daily Hooper wellness self-check.
ACWR calculator
Acute:chronic workload ratio from four weeks of load, with the sweet spot and its caveats.
OpenHRV baseline calculator
A log-based 7-day HRV average, your normal range and day-to-day variation.
OpenTraining load calculator
Weekly session-RPE load, monotony and strain from how hard each session felt.
OpenTRIMP calculator
Banister's heart-rate training impulse for any session.
OpenHooper index calculator
Sleep, stress, fatigue and soreness ratings summed into one daily wellness score.
OpenHRV by age
Short-term HRV norms by age and sex, with a checker for your SDNN or RMSSD.
OpenApple Watch HRV explained
Why Apple Watch reports SDNN, why it can look low, and how to read it.
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Sleep and caffeine
Bedtimes, naps, how much sleep you need, sleep efficiency, your chronotype, social jet lag, travel jet lag, daily caffeine and when to stop coffee.
Caffeine cutoff calculator
Estimate the caffeine left at bedtime and the latest time to finish coffee or pre-workout.
OpenSleep calculator
Bedtimes for your alarm, wake times for your bedtime, and a 7-night sleep debt total.
OpenDaily caffeine calculator
Add up today's caffeine and compare it with the 400 mg daily limit.
OpenNap calculator
Alarm times for 10-, 20-, 30- and 90-minute naps.
OpenSleep efficiency calculator
Time asleep ÷ time in bed, against the 85% marker.
OpenHow much sleep do I need?
Recommended hours of sleep for your age, and how you compare.
OpenChronotype quiz
Five-question rMEQ: are you a morning type, an evening type or neither?
OpenSocial jet lag calculator
The gap between your weekday and weekend sleep timing, from mid-sleep.
OpenJet lag calculator
Days to adjust by time zones crossed and direction, from the CDC's adaptation rates.
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Nutrition
Calories, deficits, bulking, energy availability, macros, protein per day and per meal, fiber, sugar, salt, saturated fat, glycemic load, calcium, vitamin D, iron, magnesium, potassium, zinc, vitamin C, vitamin B12, folate, omega-3, fuel during exercise, water, alcohol, carb loading, creatine and caffeine for training, from published equations and reference intakes.
Protein calculator
Daily protein in grams for muscle gain, from the meta-analysis breakpoint and the ISSN range.
OpenTDEE calculator
Daily calories burned from your resting rate and activity level, with an honest range.
OpenBMR calculator
Resting calorie burn from two published equations, compared side by side.
OpenMacro calculator
Grams of protein, carbs and fat for your calories, inside the official reference ranges.
OpenWater intake calculator
Daily water from the reference intakes, plus your own sweat rate from a weigh-in.
OpenCalorie deficit calculator
How long a deficit takes, from the 3,500-calorie rule and a model of how the body adapts.
OpenFiber intake calculator
Daily fiber from the US adequate intakes and the UK's 30 g recommendation.
OpenAlcohol units calculator
UK units, US standard drinks, grams and calories for any drink.
OpenCarb loading calculator
Grams of carbs a day before a marathon or long race.
OpenCreatine calculator
Loading and daily creatine doses for your body weight.
OpenPre-workout caffeine calculator
The caffeine dose studied for exercise, for your weight.
OpenSalt to sodium converter
Salt and sodium in g, mg or mmol, against the WHO limit.
OpenSugar intake calculator
Your daily free sugars limit from the WHO guideline.
OpenGlycemic load calculator
Glycemic load of a portion from its GI and carbs.
OpenEnergy availability calculator
Energy left after training, per kg of fat-free mass.
OpenProtein per meal calculator
Grams of protein per meal for muscle gain, from body weight and meal count.
OpenSaturated fat calculator
Daily saturated fat limit in grams from the WHO 10% ceiling.
OpenKatch-McArdle calculator
Resting calories from fat-free mass, for people who know their body fat.
OpenBulking calculator
Weekly weight gain and calorie surplus for building muscle.
OpenCarbs per hour calculator
Grams of carbohydrate per hour and in total for a training session or race.
OpenCalcium intake calculator
Daily calcium by age and sex, with the upper limit.
OpenVitamin D intake calculator
Daily vitamin D in IU and micrograms by age, with the upper limit.
OpenIron intake calculator
Daily iron by age, sex, pregnancy and diet, with the upper limit.
OpenMagnesium intake calculator
Daily magnesium by age and sex, with the supplement upper limit.
OpenPotassium intake calculator
Daily potassium by age and sex from the 2019 Adequate Intakes.
OpenZinc intake calculator
Daily zinc by age, sex and pregnancy, with the upper limit.
OpenVitamin C intake calculator
Your daily vitamin C target and upper limit, including the smoker adjustment.
OpenVitamin B12 intake calculator
Your daily vitamin B12 target by age and life stage.
OpenOmega-3 intake calculator
Daily ALA by age and sex, and what is known about EPA and DHA.
OpenFolate intake calculator
Daily folate in mcg DFE, plus the folic acid upper limit.
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Training
Weekly exercise minutes, pace, cadence, race predictions, VDOT, critical power and speed, beep and Yo-Yo tests, jump power, grip strength, deload timing, running and cycling calories, swimming and rowing paces, cycling FTP, treadmill incline, RPE, progression, plate loading, IPF GL, Wilks and Sinclair points, weekly sets and tonnage, calories burned, steps and daily step goals, hiking time, heat, humidity and cold safety and strength estimates you can work out without a lab.
One rep max calculator
Estimate your 1RM from a set of up to 10 reps with Epley and Brzycki.
OpenRunning pace calculator
Finish time to pace and speed, or pace to finish time, for any distance.
OpenRace time predictor
10K, half and marathon predictions from a recent race, with the marathon caveat.
OpenCalories burned calculator
Calories for 26 activities from your weight, with 2024 Compendium MET values.
OpenSteps to distance calculator
Steps to km or miles from your own step length, plus walking time.
OpenHeat index calculator
Feels-like temperature from heat and humidity, with NWS danger levels.
OpenRPE calculator
Weight, reps and RPE to an estimated 1RM and loads for other targets.
OpenProgressive overload calculator
When to add weight, and how much, rounded to your plates.
OpenCritical swim speed calculator
Your CSS pace per 100 m from a 400 m and a 200 m swim.
OpenRowing split calculator
Split per 500 m to watts and finish times, and back.
OpenTreadmill incline calculator
The flat-ground speed that matches your treadmill speed and incline.
OpenRunning cadence calculator
Your steps per minute, and the +5% and +10% targets.
OpenIPF GL points calculator
Your powerlifting total or bench press as official IPF GL points.
OpenBarbell plate calculator
Which plates go on each side of the bar for any target weight.
OpenFTP calculator
Functional threshold power and W/kg from a 20-minute test.
OpenWind chill calculator
Feels-like temperature from cold and wind, with the NWS frostbite warning.
OpenExercise minutes calculator
Your week's activity against the WHO 150–300 minute guideline.
OpenBeep test calculator
VO2 max from the last stage of a 20 m shuttle run.
OpenYo-Yo test calculator
VO2 max from your Yo-Yo IR1 or IR2 distance.
OpenVertical jump power calculator
Peak leg power in watts from jump height and body weight.
OpenCritical power calculator
CP and W′ from two all-out efforts, with time to exhaustion above CP.
OpenCritical speed calculator
Running critical speed and D′ from two time trials.
OpenVDOT calculator
Your VDOT from a race, with equivalent race times.
OpenRunning calories calculator
Calories burned running, from weight and distance.
OpenCycling calories calculator
Calories burned from average power and ride time.
OpenGrip strength by age
Your grip against published centiles for your age and sex.
OpenDeload planner
When your next deload is due and what athletes change in it.
OpenSinclair calculator
Your snatch plus clean and jerk total as a Sinclair total.
OpenWilks calculator
Your total or single lift as original Wilks points.
OpenTraining volume calculator
Weekly sets per muscle against the research, plus tonnage.
OpenSteps goal by age
A daily steps goal for your age from the Paluch 2022 meta-analysis, and how far you are from it.
OpenHiking time calculator
Moving time for a hike from distance and ascent, with Naismith's rule and Tobler's speeds.
OpenWBGT calculator
Wet bulb globe temperature from heat and humidity, with ACSM guidance for exercise.
OpenDew point calculator
Dew point from temperature and humidity, with the NWS summer comfort guide.
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Body
BMI, waist-to-height and waist-to-hip ratio, body roundness, ABSI, body adiposity index, relative fat mass, body surface area, body fat by tape, skinfolds or BMI, lean mass, FFMI, ideal weight, weight change, pregnancy weight gain and the fertile window, with their limits spelled out.
BMI calculator
Body mass index with standard and lower thresholds, and when not to trust it.
OpenWaist-to-height ratio
Check central fat with the 'keep your waist under half your height' rule.
OpenBody fat calculator
Body fat percentage from a tape measure with the US Navy equations.
OpenLean body mass calculator
Lean mass from height and weight with three equations, or from your body fat.
OpenFFMI calculator
Fat-free mass index and the height-adjusted value, with the 25 limit in context.
OpenIdeal weight calculator
Four classic ideal body weight formulas beside the BMI healthy-weight range.
OpenWaist-to-hip ratio calculator
Your waist-to-hip ratio against the WHO thresholds.
OpenBody roundness index calculator
Your BRI from waist and height, with what a 2024 study found.
OpenBody surface area calculator
BSA from height and weight with the Mosteller and Du Bois formulas.
OpenSkinfold body fat calculator
Body fat from three caliper skinfolds with Jackson-Pollock and Siri.
OpenBody adiposity index calculator
Body fat estimate from hips and height, no scale needed.
OpenABSI calculator
Waist size relative to your height and weight, as a z score for your age.
OpenRelative fat mass calculator
Body fat % from height and waist, no scale needed.
OpenBMI to body fat calculator
Body fat estimate from BMI, age and sex, with its limits.
OpenWeight loss percentage calculator
Percent of starting weight lost and your weekly rate, next to the NHLBI goal.
OpenPregnancy weight gain calculator
IOM 2009 total and weekly gain by pre-pregnancy BMI.
OpenOvulation calculator
Estimated ovulation and fertile days in your cycle, with how much they vary.
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Wellness timers
Focus blocks with breaks, box breathing, meditation with interval bells, stretch holds and cold plunge, each with what the research actually found.
Pomodoro timer
Focus blocks with short and long breaks, including the schedules a 2023 study tested.
OpenBox breathing timer
An animated 4-4-4-4 breathing guide, with what the 2023 trial found.
OpenMeditation timer
Preset lengths and interval bells, with an honest look at the evidence.
OpenStretching timer
A guided static stretching routine, 60 seconds per stretch per side.
OpenCold plunge timer
A countdown for cold water, with temperature classes and the cold shock risks.
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Rather not type it in?
Reps turns what your Apple Watch already records — sleep, resting heart rate, workouts — plus the meals you log into a daily read on recovery, nutrition and training.
Free to download · iPhone, iPad and Apple Watch
Looking for explainers instead? Read the recovery and HRV guides.