Heart rate variability is the variation in time between consecutive heartbeats. A healthy heart does not tick like a metronome — the interval shifts continuously as the autonomic nervous system balances sympathetic and parasympathetic input. More variation generally indicates a nervous system that can respond flexibly to demand. Less indicates one that is already loaded.
The first thing everyone wants after seeing their number is a benchmark. That instinct is reasonable and mostly unhelpful, and it is worth understanding why before looking at the table.
#### rMSSD is the metric that matters here
There are dozens of HRV metrics. The one reported by essentially every consumer wearable — Garmin, Oura, Whoop, Polar, Apple Watch — is **rMSSD**, the root mean square of successive differences between beats.
Shaffer and Ginsberg’s 2017 overview in *Frontiers in Public Health* explains why it dominates short recordings: rMSSD primarily reflects vagally mediated (parasympathetic) activity, and it is markedly less sensitive to recording length and less noisy than most alternatives. For a two-minute morning reading, it is the metric with the best signal-to-noise ratio.
#### The published age norms
Nunan, Sandercock and Brodie pooled 44 studies covering 21,438 healthy adults for *Pacing and Clinical Electrophysiology* in 2010 — still the most-cited normative reference for short-term HRV. Approximate median rMSSD by age:
| Age | Median rMSSD |
|—|—|
| Under 30 | ~42 ms |
| 30s | ~38 ms |
| 40s | ~32 ms |
| 50s | ~27 ms |
| 60s | ~22 ms |
| 70+ | ~19 ms |
The decline with age is real and expected. It reflects reduced vagal tone and increased arterial stiffness, and it is not something to fix.
#### Why the table is less useful than it looks
Those are medians of wide distributions. The healthy range at any age spans roughly a threefold spread — two people of the same age, both perfectly healthy and equally fit, can differ by 30 ms. Genetics accounts for a substantial share of that, and nothing about your training or habits will move you into someone else’s genetic band.
Three further problems with cross-person comparison:
**Devices are not interchangeable.** A chest strap sampling R-R intervals directly and a wrist optical sensor inferring them from blood volume changes will not produce the same number. Nor will two wrist devices using different proprietary filtering. Comparing your Oura figure to a friend’s Whoop figure is comparing two different measurements that happen to share a name.
**Conditions dominate.** rMSSD is sensitive to posture, time of day, breathing rate, whether you have been awake for two minutes or twenty, and whether you spoke during the reading. Slow, deep breathing can substantially raise a reading on its own. A measurement taken standing will differ from one taken lying down in the same person minutes apart.
**Recent state overwhelms baseline.** Alcohol the previous evening, a hard training session, a poor night, the onset of a cold, or a stressful day will all suppress rMSSD — often more than the difference between age bands.
#### What to do instead
Compare yourself to yourself, under fixed conditions.
1. **Same time, same position.** First thing in the morning, before getting up, after at least five minutes lying still.
2. **Same device, always.** Switching devices resets your baseline; treat it as starting over.
3. **Establish a baseline over two to three weeks** before drawing any conclusion. A single reading carries almost no information.
4. **Watch the rolling average, not the daily number.** A seven-day average moving down over two weeks is a signal. Yesterday being 8 ms below the day before is noise.
5. **Interpret alongside context.** HRV tells you that your system is loaded. It does not tell you why. Sleep, training, illness, alcohol and psychological stress all produce the same downward move.
#### The one comparison worth making
Your own trend against your own baseline, with the direction mattering more than the magnitude. A consistently rising or stable rMSSD suggests you are absorbing your current load. A sustained decline over one to two weeks, especially alongside worse sleep or elevated resting heart rate, suggests you are not — and that is worth acting on before it becomes an injury or an illness.
Our [HRV Recovery Score](/hrv-calculator/) scores a reading against these Nunan age references and combines it with resting heart rate, sleep and subjective readiness. The composite weighting is our own judgement rather than a validated model, and the page says so, along with the research the age references come from.
**References:**
*Nunan D, Sandercock GRH, Brodie DA. A Quantitative Systematic Review of Normal Values for Short-Term Heart Rate Variability in Healthy Adults. Pacing and Clinical Electrophysiology. 2010;33(11):1407–1417.*
*Shaffer F, Ginsberg JP. An Overview of Heart Rate Variability Metrics and Norms. Frontiers in Public Health. 2017;5:258.*