HRV calculator
Two ways to use it: paste beat-to-beat intervals to compute RMSSD, SDNN and pNN50, or enter an RMSSD you already have and your age to see the typical range.
Nothing you type leaves your device. No sign-up, no limits.
| Age | Typical resting RMSSD |
|---|
General wellness information, not medical advice. Results are estimates based on published formulas and ranges; they are not a diagnosis. Read more.
How to use the hrv calculator
- Paste R-R intervals if you have them. Many HRV apps and chest straps export beat-to-beat intervals in milliseconds. Paste them and the calculator computes RMSSD, SDNN, pNN50 and mean heart rate.
- Or enter an RMSSD you already know. Most apps, including Pulse Tracker, report RMSSD as the headline HRV number.
- Enter your age. HRV falls with age, so the typical range is shown for your decade.
- Compare with yourself over time. The range is only orientation. Your own 7-day trend is more informative than any table.
What the three metrics mean
RMSSD is the root mean square of successive differences between beats and reflects parasympathetic (vagal) activity; it is the standard for short readings. SDNN is the overall standard deviation of intervals and captures slower influences too. pNN50 is the percentage of successive intervals that differ by more than 50 ms. All three rise with recovery and fall with stress, illness and fatigue.
How to get a clean reading
Measure in the morning before caffeine, seated or lying down, breathing normally, for at least one minute (30 seconds is acceptable for RMSSD). Keep still: movement artifacts inflate every HRV metric. Use the same method daily.
Wellness disclaimer. Pulse Tracker is intended for general wellness use only. It is not a medical device, is not FDA cleared or approved, and is not intended to diagnose, treat, cure or prevent any disease or condition. Blood pressure shown in the app is either a value you entered from your own cuff or an estimate derived from the pulse signal after cuff calibration; it is not a measurement and must not be used to make medical decisions. Read the full wellness disclaimer. Camera readings, estimates and classifications are for general information only and can be affected by movement, lighting, skin temperature and other factors. Do not use them to diagnose, treat or make decisions about a medical condition. Always consult a qualified healthcare professional, and call emergency services if you have chest pain, shortness of breath, fainting or other urgent symptoms.
Frequently asked questions
What is a good HRV by age?
Typical resting RMSSD is roughly 40 to 100 ms in your twenties, falling to 20 to 50 ms over 60. Individual variation is huge, so compare with your own baseline.
Is a higher HRV always better?
Generally higher resting HRV means better recovery. Sudden very high values can come from ectopic beats or measurement noise rather than good recovery.
How many intervals do I need?
At least 30 seconds of clean beats for RMSSD, ideally 1 to 5 minutes. SDNN is most meaningful over 24 hours.
Can an iPhone measure HRV?
Yes, at rest with a fingertip on the camera. Pulse Tracker reports RMSSD, SDNN and pNN50 from a 30-second scan with a quality score and a 30-day baseline.
More free tools
Heart rate zone calculator
Free heart rate zone calculator. Enter your age (and resting heart rate for the Karvonen method) to get your max heart rate and all five training zones in BPM.
Open tool →Max heart rate calculator
Free max heart rate calculator. Enter your age to compare four published formulas: 220 − age, Tanaka, Gulati for women and Nes, and see your target heart rate ranges.
Open tool →Blood pressure calculator
Free blood pressure calculator. Enter systolic and diastolic to get the American Heart Association category, pulse pressure and mean arterial pressure, with what each result means.
Open tool →MAP calculator
Free mean arterial pressure calculator. Enter systolic and diastolic to get MAP and pulse pressure instantly, with the normal ranges and the formula explained.
Open tool →Tap BPM counter
Free online heart rate counter. Find your pulse at the wrist, tap the button with each beat, and see your BPM live. Or use the 15-second count mode. No camera, no sign-up.
Open tool →Breathing pacer
Free online breathing pacer. Follow the expanding circle for resonance breathing at 5.5 breaths per minute, box breathing or 4-7-8, with a session timer. No sign-up.
Open tool →Measure instead of calculating
Pulse Tracker reads your heart rate, HRV and respiratory rate from the iPhone camera in 30 seconds. Free, no account.
Download for iPhoneRequires iOS 17 or later · ★ 4.7 rating · Available in 8 languages