Apple Watch has been measuring HRV since the first model. It is just easy to miss, and the raw numbers can look random until you know how they are taken.
Where to find it
On your iPhone: Health, Browse, Heart, Heart Rate Variability. You will see a daily value and a chart. The watch’s own Heart Rate app does not show HRV. If you want it on your wrist, that takes a third party app or complication.
How Apple measures it
Apple Watch reports HRV as SDNN, the standard deviation of the gaps between heartbeats over a short sample, usually about a minute. It takes these samples on its own schedule, mostly when you are still and mostly overnight, plus one during a Breathe or Mindfulness session. That is different from a strap that records every beat all night and computes rMSSD from adjacent beats. Both are HRV. They are not the same number, and you should never compare an Apple Watch SDNN with a WHOOP or Oura rMSSD directly.
Why it jumps around
Short samples land on whatever your body is doing at that moment. A deep breath, a turn in bed, a dream: all change the reading. So a single night’s HRV on Apple Watch is noisy. Two fixes:
- Wear it to bed. Overnight samples are the calm ones.
- Look at the trend. Seven day and thirty day averages are stable enough to act on. Single readings are not.
What is a good number
There is no good number that applies to everyone. HRV falls with age, varies with fitness and sleep, and the spread across healthy people is wide. What matters is your own baseline. Sixteen builds one from your overnight readings and draws a normal band around it, so a dip reads as a dip for you rather than against a stranger’s average. When HRV sits under your band for several days with a raised resting heart rate, that is the signal: back off, sleep, check whether you are getting ill.
Turning HRV into something useful
Sixteen reads the Health app’s HRV samples along with resting heart rate, sleep and respiratory rate, and turns them into a recovery score each morning. That score sets your strain target for the day. If you have set up screen time rules, a bad recovery keeps your locked apps locked a little longer. The HRV page shows what the screen looks like, and how to improve HRV covers what actually moves the number.
