There is no universal “normal” HRV. Published adult values for the most common measure (RMSSD) span roughly 20 to 100 milliseconds, and healthy people sit anywhere across that whole band. HRV is one of the most individual metrics in consumer health: age, genetics, resting heart rate, medication, alcohol, sleep and fitness all move it, and two equally healthy people can differ by a factor of three. The number worth watching is your own rolling baseline, not a chart. A meaningful change is a sustained shift away from your personal norm — typically a drop of roughly 20% or more below your own average across several days.
Why no chart can tell you your normal
HRV is a measure of variation in the time between heartbeats. It is not a fitness score, and it is not standardised across devices: an Apple Watch, a chest strap and a phone-camera app can each produce a different number for the same person in the same minute, because they measure over different windows and use different statistics. Published “normal” tables usually come from small samples using specific equipment, which is why they disagree with each other and with your watch.
| Question | Honest answer |
|---|---|
| Is there a normal range for adults? | Roughly 20–100 ms RMSSD in published samples — but the spread within healthy people is so wide that a single number tells you almost nothing. |
| Does HRV fall with age? | Yes on average — population studies consistently report lower average HRV at older ages. It does not mean a lower reading is abnormal for you. |
| Do athletes have higher HRV? | Often, but not reliably. Training load suppresses HRV in the short term; endurance athletes can also have very low resting heart rates that change the picture. |
| Is higher always better? | No. Extremely high or erratic readings can reflect arrhythmia or measurement artefact. Against your own baseline, higher usually accompanies better recovery. |
Why your number disagrees with everyone else's
Even with identical heartbeat data, two apps can report different HRV numbers, because they summarise the intervals with different statistics. The Apple Watch's original HRV reading in Apple Health is SDNN — the standard deviation of all heartbeat intervals in the window. Most recovery apps, and every other major wearable (Oura, WHOOP, Garmin, Fitbit, Pixel Watch), report RMSSD instead, which looks only at the difference between consecutive beats and tracks short-term parasympathetic activity. Apple added a second measure, Recovery HRV (RMSSD), in September 2026 — but only on Apple Watch Series 12 and Ultra 4. Older models keep recording SDNN.
The two are not interchangeable, and no formula converts one into the other. In a well-described reference study of 1,906 healthy adults measured with five-minute resting ECG (Voss et al., PLOS ONE, 2015), mean SDNN ran only about 1.1 to 1.6 times mean RMSSD depending on age — and both fell with age: men aged 25–34 averaged 50.0 ms SDNN and 39.7 ms RMSSD, and by 65–74 the averages were 29.6 and 19.1 ms. The point is not the table. The point is that the same night, read by two devices, produces two different numbers that are both correctly computed.
So never mix them in one trend line. If your app reports RMSSD, follow its RMSSD. If you read Apple Health's SDNN, follow that. Your number differing from a friend's Oura says nothing about either of you.
What actually matters: your own baseline
- 1Measure at the same time every day. Overnight or first-thing-on-waking is the usual choice, because conditions are consistent.
- 2Let a baseline build. Two to four weeks of consistent overnight wear before any number means much.
- 3Watch the trend, not the day. A single low morning is noise. Several days below your norm is signal.
- 4Never compare across apps. Different statistics and windows mean the same morning can produce two different numbers. Pick one app.
What moves HRV day to day
- Suppress it: poor or short sleep, alcohol, illness (often before you feel symptoms), hard training, dehydration, late eating, heat, psychological stress.
- Raise it: consistent sleep, easy training days, good aerobic fitness over months, slow nasal breathing, and simply recovering.
- Confuse it: a loose watch strap, movement during measurement, irregular rhythm, and switching devices or apps.
Because so much moves it, a lone HRV number is a weak signal. It becomes useful folded together with resting heart rate and sleep — which is exactly what a recovery score does.
What the research says about low HRV and mortality
HRV is not just a fitness signal. A 2022 systematic review and meta-analysis (Jarczok et al., Neuroscience & Biobehavioral Reviews) pooled 32 studies plus two individual-participant datasets — 38,008 participants across general and clinical populations — and found that lower HRV was a significant predictor of higher all-cause mortality. In the sub-analysis of 5-minute RMSSD, sitting in the lowest quartile corresponded to a 56% higher risk of death (HR 1.56, 95% CI 1.32–1.85) compared with the other quartiles.
Read that carefully: it is a population-level association from observational data, mostly drawn from five-minute clinical recordings — not a prediction about you, and not a reason to panic over one low night. What it does tell you is why researchers keep studying HRV, and why the trend of your own number, measured consistently, is the thing worth watching.