HRV by Age

A good HRV is one that is normal for you, and it falls with age. In a study of 8 million Fitbit users, the median early-morning RMSSD was 66 ms for men aged 20–21, 38 ms at 40–41 and 27 ms at 60–61 (women: 56, 37 and 28 ms). Half of people sit outside the middle range, so your own trend matters more than any chart.

Heart rate variability (HRV) is the small change in time between one heartbeat and the next. A heart at 60 beats a minute does not tick once a second like a clock; some gaps are a little longer, some a little shorter. That variation is steered by the autonomic nervous system, the part that speeds you up under strain and slows you down to rest, which is why so many watches and rings now use it as a daily read on recovery.

1. Pick the device your number comes from. The checker knows which measure each one reports. 2. Enter your age and, if you like, your sex. RMSSD barely differs between women and men, but SDNN does. 3. Enter the number from this morning, in milliseconds. 4. See where it sits among people your age, with the 25th percentile, median and 75th percentile marked. 5. Log it with how you feel, on a 0 to 10 scale. After five mornings, your HRV and your mood appear on one chart.

Nothing leaves your browser. Your age, device and readings stay on this device, so tomorrow the checker opens ready for one new number.

The main comparison comes from Natarajan and colleagues (The Lancet Digital Health, 2020), who analysed wrist readings from 8.2 million Fitbit users and published reference tables by age and sex. We use their early-morning figures, taken from 5-minute readings between 6 and 7 am, because that is the closest match to the overnight and morning numbers most devices show. “Middle half” means the 25th to 75th percentile: half of people that age were inside it, a quarter below and a quarter above.

The result also shows a lab reference from Voss and colleagues (PLOS ONE, 2015): 1,906 healthy adults recorded on a 5-minute ECG while lying down. Lab readings are short and taken awake, so they run lower than most watch numbers. Neither table is a line between healthy and unhealthy. Plenty of well people sit in the lower quarter, and plenty of people with high numbers are simply fit.

Devices do not measure the same thing. Apple Health stores HRV as SDNN, the spread of all the gaps between beats in a short reading. Oura, WHOOP, Garmin, Polar and Fitbit report RMSSD, which looks at how much each gap differs from the one before. The two are not interchangeable, and SDNN usually reads higher, which is why the checker uses a separate SDNN table for Apple Watch.

Timing matters just as much. Oura averages 5-minute samples across your sleep, WHOOP weights deep sleep more heavily, Polar uses roughly the first four hours of the night and Fitbit uses your longest sleep. WHOOP’s own member data puts the middle half of 25-year-old men at roughly 50 to 100 ms, well above the Fitbit morning figures, which shows how much the method changes the number. If your app only shows a 0 to 100 HRV score, as Elite HRV does, look for the RMSSD underneath it. For more on Apple’s side, see does Apple Watch track stress?

In the Fitbit data, every HRV measure declined steadily from the twenties to the sixties, and readings followed a strong daily rhythm, with early-morning numbers well above evening ones. People who took more steps had higher HRV at every age, though a study of one day per person cannot show which causes which.

From night to night, the usual movers are a short or broken night, alcohol, a hard or late workout, getting ill, caffeine and a demanding day. Polar puts it simply: after a heavy day, it takes your body longer to switch from activation into rest while you sleep. That is why a single low reading means little, and a run of them alongside feeling worn out is worth noticing. Our guide to low HRV covers the common reasons, and what is a good HRV goes deeper on the ranges.

Oura, WHOOP and Garmin all tell members the same thing: compare your HRV with your own history, not with other people. Garmin’s HRV Status needs about three weeks of nights before it settles on your personal range. The checker does a lighter version of this. After three saved mornings it shows your recent average and how today compares, so a drop of a few milliseconds after a late night stops looking like news, and a week well under your usual stands out.

HRV describes your body, not your mood, and the two do not always move together. Some people find that their best mornings and their highest HRV line up; others see no link at all. Logging both is the only way to find out which kind you are, and the chart makes the pattern visible after five mornings. To see your body next to the rest of your week, pair this with the mood tracker or the 60-second mental health check-in, and check how your nights add up with the sleep calculator.

HRV from a watch or ring is a wellness estimate, not a medical test, and this checker cannot say anything about your heart’s health. Population ranges come from one device and one time window, so use them as a rough guide only. Medicines that affect heart rate change HRV too, which is why the lab study left out people taking them. If you have chest pain, fainting, a racing or irregular heartbeat, or breathlessness, see a doctor rather than a chart.

If your number has been sliding and you feel it too, start with the dull levers: sleep, alcohol, training load and the pace of your days. Our guide on how to improve HRV goes through them one by one, and a five-minute vagus nerve reset or box breathing is an easy way to give your body a calmer few minutes. To see what your watch’s stress or recovery score means next to how you feel, try the stress score checker.