Apple Watch Series 12 and Ultra 4 show two kinds of heart rate variability (HRV). Apple says Recovery HRV is best for daily signals of stress and recovery, and overall HRV is best for insights into your broader health, including cardiovascular health. Apple has not published how either one is calculated, so treat them as two separate numbers and compare each only with its own past values.
Apple’s pages checked: 20 October 2026. We will update this page when Apple documents more about how the two numbers work.
What each number is for
Apple announced both numbers on 9 September 2026, with the new Health Sensing System in Apple Watch Series 12 and Apple Watch Ultra 4. Apple says the watch now measures HRV as often as every five minutes and shows it in a new section of the Heart Rate app.
| Recovery HRV | Overall HRV | |
|---|---|---|
| What Apple says it is best for | Daily signals of stress and recovery | Insights into broader health, including cardiovascular health |
| Compared with your personal baseline Baseline Your own usual HRV level and range, built from weeks of readings taken the same way. Comparing a reading with your baseline says more than comparing it with other people. More about Baseline | Yes, in overnight vitals | Apple has not said |
| Watches Apple lists it with | Series 12 and Ultra 4 | Series 12 and Ultra 4 |
| Formula published | No | No |
Recovery HRV is the number for day-to-day reading. Apple’s support page describes it as a measure of how the time between heartbeats varies, one that can be an indicator of stress and recovery. Overnight vitals now include Recovery HRV, analysed against your personal baseline, and Apple says HRV is sampled while you are still.
Overall HRV answers a slower question: what your HRV says about your health in general. Apple does not say more than that, so read it as a trend over weeks rather than night by night.
watchOS 27 runs on Apple Watch Series 9 or later, SE 3 and Ultra 2 or later, but Apple lists the more frequent HRV, Recovery HRV and readiness with Series 12 and Ultra 4.
Why the two numbers differ
Apple has not said which statistic either number uses, or over which stretch of time. It has described two different jobs. Recovery HRV is compared with your baseline overnight and should move with stress and recovery. Overall HRV is meant to describe your health more broadly. If Apple calculates them differently, as those jobs suggest, they will not match even when they start from the same heartbeats.
For years, Apple Health has stored Apple Watch HRV as SDNN SDNN The standard deviation of all NN intervals in a recording, in milliseconds. It measures overall variability, and its value depends strongly on how long the recording lasts. More about SDNN . Apple’s developer documentation says HealthKit uses SDNN, the standard deviation of the intervals between normal heartbeats, and that the system records samples automatically on Apple Watch. Some reports suggest Recovery HRV works more like RMSSD RMSSD Root mean square of successive differences: an HRV metric built from how much each heartbeat interval differs from the next, in milliseconds. It mainly reflects vagal activity. More about RMSSD (Gadgets & Wearables, 2026), partly because Apple’s HealthKit documentation for iOS 27 lists a new data type named for RMSSD. That page has no description, and Apple has not said what it holds, or whether overall HRV is the same SDNN value Health already stores. Until Apple says so, both ideas are guesses.
Why neither matches your ring or strap
Most rings and bands report RMSSD measured during sleep. RMSSD looks only at the change from one beat to the next. SDNN counts every kind of variation in a recording, including slow drifts in heart rate, and it depends on how long the recording lasts, so SDNN values from recordings of different lengths should not be compared (Task Force, 1996). The lesson on RMSSD, SDNN and lnRMSSD shows how each one is calculated.
Even if Recovery HRV turns out to be RMSSD, it will not line up with a ring’s number. Each device measures over a different part of the night and cleans the beats in its own way, which is why Oura and WHOOP show different HRV although both report RMSSD. Why is Apple Watch HRV different? covers the older Apple value against other brands, and the HRV by device guide lists what each brand measures and when.
Compare each number only with itself
- Keep two trends. Look at Recovery HRV against your past Recovery HRV, and overall HRV against your past overall HRV. One can rise on a day the other falls.
- Start fresh on a new watch. Apple has not said how the new numbers relate to the HRV an older Apple Watch recorded, so begin a new trend on Series 12 or Ultra 4 instead of joining the two.
- Give the baseline time. Overnight vitals compare Recovery HRV with your personal baseline, and any baseline is shaky for the first weeks. See how long until an HRV baseline is reliable.
- Keep other brands separate. A ring’s or strap’s number sits on its own scale, even on the same night.
Where the readiness score fits
Series 12 and Ultra 4 also add readiness: one score from 0 to 10 each day, with one of four suggestions, from “Recover” to “Go For It”. Apple says it looks at your recent activity, training load, vitals and sleep score, and that it updates through the day as new data comes in. Vitals include Recovery HRV, so HRV can feed into the score, but Apple has not published how much weight any one input carries. Which recovery score should I trust? looks at scores like this across brands.
What Apple has not said yet
As of 20 October 2026, Apple has not published:
- the formula for Recovery HRV or for overall HRV;
- whether overall HRV is the SDNN value Health has stored for years;
- any ranges or typical values for either number, so a chart that claims a “normal” Recovery HRV is not based on anything Apple has released;
- how much weight HRV carries in the readiness score Readiness score A single number, often out of 100, that a device builds from your HRV, resting heart rate, sleep and other inputs to suggest how ready you are for the day. The weighting is not published. More about Readiness score .
We will update this page when Apple documents any of these.