Can you compare your HRV with a friend's, or with an age chart?

Sort of, but not really. Across big groups, HRV does fall with age, and lower averages go with more heart disease. For one person, though, the spread is huge: healthy people of the same age differ ten times over, and every device measures it a little differently. Compare yourself with yourself.

Why it’s tempting

Every other number comes with a chart. Blood pressure has categories. Cholesterol has targets. So when your friend’s ring says 72 and yours says 28, it feels like you’re losing. Age charts online look official, with a neat line for each decade.

Is comparing HRV like comparing voices?

Sort of. Picture asking a room of healthy people to say “ah”, then ranking their health by how deep their voice is. Voices differ a lot between healthy people, and the ranking would tell you nothing. But if your own voice is hoarse one morning, you notice at once, because you know how you usually sound.

HRV is like that. The difference between you and your friend is mostly who you are. The difference between you this week and you last month is what’s worth noticing.

How wide is normal?

A 2010 review pooled 44 studies of 21,438 healthy adults to set normal values for short recordings. It found very large differences between individuals, and values that shifted with how the beats were cleaned and recorded. A 2017 review warns that norms from 24-hour, 5-minute and shorter recordings can’t be swapped for one another. Your ring’s overnight average is yet another kind of recording.

Why devices make it worse

Apple Watch reports SDNN. Oura, WHOOP and Garmin report RMSSD. Those are different measurements of the same beats, so an Apple number next to a ring number compares two different things.

Even between rings and bands that report the same measurement, a 2025 overnight test against a chest strap found average errors from 6 to 16 percent across five devices. In 103 athletes, an optical sensor gave an average RMSSD of 81 ms where an ECG on the same people gave 104. Your friend’s device and yours may not agree on the same heart.

The best case for the chart

“Big studies show lower HRV means more heart disease, so where I sit must matter.” In a 2013 pooled analysis of 21,988 people, those with the lowest SDNN had a 35 percent higher risk of a first cardiovascular event than those with the highest. That’s real, across groups. It doesn’t turn one overnight number from one wearable into a grade, and plenty of healthy people sit at the low end of any chart.

And age does matter for the slow drift. In a 1998 study of 260 healthy people, 24-hour RMSSD in people in their fifties was about half of teenage values. So a 55-year-old shouldn’t expect their twenties back, and doesn’t need to.

What to compare instead

Your own weekly average. In 10 runners over nine weeks, the weekly average of each runner’s own HRV lined up closely with how much their 10 km time improved, while single days barely did. Each runner was measured against their own starting point, and that was enough to tell the story.