Apple Watch, readiness & HRV
How to see your HRV on Apple Watch and iPhone
Your Apple Watch measures heart rate variability (HRV) in the background, mostly while you sleep, and saves every reading to Apple Health. The numbers are there, but they are easy to miss and hard to read: one value jumps 20 ms from one day to the next, and a “good” HRV for one person is a low one for another. Here is where to find yours, what it measures and how to read the trend instead of the noise.
Short answer
On iPhone, open the Health app, tap Browse (or Search on newer iOS versions), then Heart, then Heart Rate Variability. On the watch, open the Heart Rate app and turn the Digital Crown. Apple Watch reports HRV as SDNN in milliseconds. Compare it with your own usual range over weeks, not with other people and not day to day.
How to see HRV in the Health app
- Open the Health app on your iPhone.
- Tap Browse, or Search on newer iOS versions, and choose Heart.
- Tap Heart Rate Variability. Switch between D, W, M, 6M and Y to see days, weeks, months and longer.
- Tap Add to Favorites at the bottom if you want it on the Summary page.
On the watch itself, open the Heart Rate app and turn the Digital Crown to scroll to HRV. Newer watches also show overnight values in the Vitals app, which compares last night’s heart rate, breathing rate, wrist temperature, blood oxygen and sleep with your usual range.
No readings? Wear the watch to bed with sleep tracking on, keep Heart Rate turned on in Settings, Privacy & Security, Health on the watch, and make sure the band sits snugly. The watch measures when you are still, so a restless night gives fewer values.
What Apple Watch measures: SDNN
HRV is the variation in time between heartbeats. Apple Watch reports it as SDNN, the standard deviation of those intervals over a short recording. Polar, WHOOP, Oura and Garmin report RMSSD, a different calculation. The two move in the same direction but can’t be converted into each other, so an SDNN of 45 ms and an RMSSD of 45 ms don’t mean the same thing. Our guide to SDNN vs RMSSD explains the difference.
What is a normal HRV?
There is no single normal value. HRV depends on age, genetics, fitness and the method of measurement, and healthy adults can sit anywhere from the 20s to above 100 ms. It tends to be higher in younger and fitter people and falls gradually with age. That is why comparing your number with a friend’s, or with a chart online, tells you little.
What does tell you something is your own pattern:
- Your usual range. Look at the last month or two. Most readings fall inside a band; that band is your normal.
- A weekly average. The 7-day average moves far less than single readings and shows real shifts.
- Several low nights in a row. One low night after a late dinner or a glass of wine is common. Several nights below your range, together with a higher resting heart rate, are worth noticing.
What moves your HRV
| Usually lowers HRV | Usually supports it |
|---|---|
| Hard or unusually long training | Easy days after hard ones |
| Short or broken sleep | Regular, sufficient sleep |
| Alcohol, especially in the evening | Consistent aerobic training over months |
| Getting sick, stress, travel, heat | Good hydration and recovery |
A lower HRV after a big training block is expected and usually rebounds within a few days. A drop that stays without an obvious reason, or that comes with symptoms, is a reason to talk to a doctor. HRV is a useful signal, not a diagnosis.
Read your HRV in context with Keho
The Health app shows the readings. Keho reads the same HRV from Apple Health and puts it next to the numbers that explain it. Every morning it compares last night’s HRV, resting heart rate and sleep with your own usual range and your recent training load, and turns them into a readiness score from 0 to 10 with the reasons in plain words, such as “HRV 18% above your usual”. HRV gets its own tile with last night’s value, your usual range, the last seven nights and a trend arrow.
On iOS 27, Keho uses the Apple Watch’s overnight Recovery HRV when your watch records one. Polar owners get their own RMSSD values kept as RMSSD; Keho never relabels them as SDNN. Everything is calculated on your iPhone, with no account. For more on the score itself, read a readiness score for Apple Watch, and for the companion metric, your resting heart rate trend.
Questions
Why does my HRV change so much from day to day?
Each reading is a short recording, and HRV reacts to sleep, alcohol, stress and even posture. Day-to-day swings of 10–20 ms are normal. Read the weekly average and your range.
When does Apple Watch measure HRV?
Several times a day when you are still, and most reliably during sleep. Breathe sessions in the Mindfulness app also record a reading.
Is a higher HRV always better?
Within your own range, higher usually means better recovered. A sudden value far above your normal can also come from an irregular rhythm or a bad recording, so trends matter more than any single peak.