What’s the difference between HRV and Recovery HRV on Apple Watch?

What Recovery HRV is

Apple says Recovery HRV measures how the time between heartbeats varies, and can be an indicator of stress and recovery. It is sampled while you are still, so how many readings you see depends on how active you are. You find it in the Heart Rate app on the watch by turning the Digital Crown.

Apple lists Recovery HRV for Apple Watch Series 12 and Apple Watch Ultra 4 only. Installing watchOS 27 on an older watch does not add it. The same two models get Apple’s Readiness score, which uses HRV among its overnight vitals. Here’s which Apple Watches get a readiness score.

What the older HRV figure is

Apple Health has stored Apple Watch HRV as SDNN since 2017. Apple’s developer documentation describes SDNN as the standard deviation of heartbeat intervals. Every Apple Watch that records HRV saves this figure, and it is the number most Apple Health apps have read.

SDNN and RMSSD, in plain words

Both are ways of putting a number on how much the gaps between heartbeats vary.

• SDNN looks at the overall spread of the gaps across a recording. It depends a lot on how long the recording is, so a short sample and a 24-hour one give very different figures.
• RMSSD looks at how much each gap differs from the one before it. It mostly reflects quick, beat-to-beat changes linked to the parasympathetic ("rest and digest") side of the nervous system, which is why it is often used for day-to-day recovery.

In iOS 27, Apple added an RMSSD type to HealthKit alongside SDNN. Apple has not said in its support pages that Recovery HRV is RMSSD, so treat that link as likely rather than confirmed.

Why your two numbers don’t match

SDNN and RMSSD are different calculations, so the same heartbeats give two different figures. Other wearables measure differently again. WHOOP says it uses RMSSD measured during sleep. Oura says its HRV is the average of five-minute samples taken while you sleep. Apple’s long-standing figure is SDNN. A number from one device, or one metric, is not directly comparable with another.

What tells you most is your own trend in one metric over days and weeks. Sleep, alcohol, stress, illness, hard training and the time of day all move HRV, and one low reading on its own says little. Here’s what a low HRV can mean.

Which one should you watch?

If you have a Series 12 or Ultra 4, Apple says Recovery HRV can be an indicator of stress and recovery. On any other Apple Watch, the SDNN figure in Apple Health is what you have. Either way, compare it with your own usual, not with someone else’s number. Published ranges by age use specific recordings, so they are only a loose guide. You can see typical HRV by age for SDNN from a published study.

Vital gives general information about fitness and wellbeing. It is not medical advice, and it does not diagnose or treat any condition.