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.

• Resting heart rate by age

  See where your resting heart rate falls among people your age and sex, using national NHANES percentiles.

  Open

• VO2 max by age

  Compare your Apple Watch Cardio Fitness with measured treadmill VO2 max percentiles by age and sex.

  Open

• Heart rate recovery

  Calculate your one-minute heart rate recovery and see how Apple Watch Cardio Recovery is measured.

  Open

• Caffeine cutoff calculator

  Estimate the caffeine left at bedtime and the latest time to finish coffee or pre-workout.

  Open

• Sleep calculator

  Bedtimes for your alarm, wake times for your bedtime, and a 7-night sleep debt total.

  Open

• Protein calculator

  Daily protein in grams for muscle gain, from the meta-analysis breakpoint and the ISSN range.

  Open

• ACWR calculator

  Acute:chronic workload ratio from four weeks of load, with the sweet spot and its caveats.

  Open

• HRV by age

  Short-term HRV norms by age and sex, with a checker for your SDNN or RMSSD.

  Open

• Apple Watch HRV explained

  Why Apple Watch reports SDNN, why it can look low, and how to read it.

  Open

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.

Download Reps on the App Store

Free to download · iPhone, iPad and Apple Watch

Looking for explainers instead? Read the recovery and HRV guides.