COROS gives you HRV two ways: Overnight HRV, which the watch records by itself while you sleep, and the Wellness Check, a short reading you start from the watch’s toolbox. They cover different stretches of time, so keep their numbers in separate series.
Documentation checked: 22 October 2026. COROS updates its watches and app often, so details can change.
What HRV number COROS shows
COROS reports 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 , the standard short-term measure of how much each gap between heartbeats differs from the next (Task Force, 1996). Its Wellness Check page names RMSSD, and its coaching article spells the method “mRSSD”, a slip for the same measure (COROS Support, Wellness Check; COROS, What is HRV?). Because the unit is milliseconds, you can set the number beside published RMSSD values, as long as you remember it is a whole-night average and not a five-minute morning reading.
COROS says that, depending on the model, HRV is measured from the optical sensor or the electrocardiogram ECG A recording of the heart's electrical activity, taken with electrodes on the skin. ECG-based RR intervals are the reference standard for measuring HRV. More about ECG ; for the Wellness Check, the APEX 2, APEX 2 Pro, APEX 4, VERTIX 2 and VERTIX 2S add their built-in electrical sensor (COROS Support, HRV; Wellness Check). COROS does not accept HRV from an external chest strap (COROS Support, HRV).
On the APEX 2, APEX 2 Pro, APEX 4, VERTIX 2 and VERTIX 2S, COROS is replacing an older HRV Index HRV triangular index The number of NN intervals in a recording divided by the height of the tallest bar of their histogram. A unitless geometric measure of overall variability that a few bad beats barely move. More about HRV triangular index with the Wellness Check, which shows HRV “as raw data (rMSSD)” (COROS Support, Wellness Check).
When COROS measures: overnight and on demand
Overnight HRV needs nothing from you beyond wearing the watch to bed. COROS says HRV “is measured continuously overnight in 10-minute intervals to provide you with an average HRV score” (COROS Support, Overnight HRV). Its coaching article argues that an average of the whole night evens out the swings between sleep stages (COROS, What is HRV?). COROS does not say how it treats brief wakes.
That whole-night window sets COROS apart from brands that read a slice of the night. In the model below, COROS averages every sleeping interval, WHOOP leans on the last deep-sleep period and Polar takes the first four hours.
Same night, different numbers
A teaching model, not a measurement
Sleep stages lights out to waking
HRV every 5 minutes (RMSSD) 20 to 60 ms
- COROS
- 47.5 ms RMSSD
An average of HRV measured in 10-minute intervals while you sleep. COROS does not say how it treats brief wakes; the model leaves them out.
Same night, same heart: COROS 47.5 ms, WHOOP 54.6 ms and Polar 44.8 ms, because each device averages different hours.
The buttons work when JavaScript is on. The window for each device is listed in the description.
Two charts over eight hours of simulated sleep. The top chart is a hypnogram stepping between awake, REM, light and deep sleep, with deep sleep mostly in the first half and REM mostly in the second. The bottom chart is a line of HRV values, one per five minutes, that rise gently through the night and dip during wakeful minutes. One button per device shades the part of the night that device averages. COROS: 47.5 ms RMSSD. WHOOP: 54.6 ms RMSSD. Polar: 44.8 ms RMSSD. Same night, same heart: COROS 47.5 ms, WHOOP 54.6 ms and Polar 44.8 ms, because each device averages different hours.
The Wellness Check is a spot reading. Press and hold the BACK/LAP button to open the toolbox, choose Wellness Check and follow the prompts; the test takes 30 to 60 seconds (COROS Support, Wellness Check). COROS recommends it “upon waking up while you are still laying on your bed”, and warns that a few minutes of walking, a glass of water or a trip to the bathroom can all change the value (COROS, What is HRV?). Wear the watch snug, two fingers above the wrist bone, and keep your forearm level and still (COROS Support, Wellness Check).
Two ways COROS reads HRV
From COROS’s documentation
Overnight HRV
- When
- Automatically, whenever you wear the watch to sleep.
- How
- HRV in 10-minute intervals, averaged into one value for the night.
- Shows
- Nightly HRV (RMSSD) in ms, with day, week and month trends.
- Against
- A normal range from your past nights, once 5 nights are in.
Wellness Check
- When
- When you start it from the toolbox. COROS suggests on waking, still in bed.
- How
- 30 to 60 seconds of optical readings; the APEX 2, APEX 2 Pro, APEX 4, VERTIX 2 and VERTIX 2S add their electrical sensor.
- Shows
- HRV (RMSSD), stress, heart rate, breathing rate and, on some models, SpO2.
- Against
- Your own earlier checks, in the COROS app.
Two panels. Overnight HRV: a night of short bars, one per 10-minute interval of sleep, joined into a single nightly value, then seven nightly values against a shaded normal range, one below it, one above it and the rest inside. Wellness Check: a night drawn as a grey line, with a short highlighted reading at waking. Under each panel, when it measures, how, what it shows and what it is compared with.
A minute in bed and a night’s average are different measurements. Overnight vs morning HRV explains why each belongs in its own series.
Overnight HRV and your normal range
After five nights, the watch shows an assessment, and your normal range “is established from previous nights HRV data”. Inside the range, COROS says, your body is “responding to stress in a typical manner”; elevated HRV “may indicate less stress”, and lower HRV “typically points to higher stress levels” (COROS Support, Overnight HRV). COROS does not publish how it calculates the range or how many nights it spans.
COROS’s coaching article turns the three outcomes into training advice (COROS, What is HRV?):
- Lower: possible causes include sickness, a poor night, anxiety or physical activity. “Easier workouts are recommended.”
- Within: your nervous system “is ready to perform high-intensity sessions.”
- Higher: possible causes include extra rest, a new workout or travel, and “additional assessment is required to conclude anything.”
COROS has no feature called HRV Status; that is Garmin’s name for its seven-day comparison. How long until my HRV baseline is reliable puts the five-night wait beside other devices.
Daily Stress, Recovery and Sleep Score
HRV goes into Daily Stress, shows up in the Sleep Score through sleep stress, and stays out of Recovery. Daily Stress, a score from 0 to 100, comes from heart rate and HRV measured every 5 minutes, set against your own 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 , which COROS says settles after about a week. A score for the whole day needs the watch on through the night and for at least 16 hours in a row, and moving your arm can push the reading up for a while (COROS Support, Daily Stress).
Recovery, the percentage on the recovery widget, rests on Training Load and Base Fitness. COROS states that sleep, HRV and Daily Stress “are not part of the Recovery calculation” (COROS Support, Recovery Widget), so Recovery can read Fresh after a night when your HRV fell below its range. Check Overnight HRV for that.
What is in a readiness score?
From the makers' own documentation
- HRV : named by the maker HRV, measured "once every 5 minutes" with heart rate.
- Resting heart rate : not named Not named by the maker.
- Breathing rate : not named Not named by the maker.
- Sleep : not named Not named by the maker.
- Temperature : not named Not named by the maker.
- Activity or load : not named Not named by the maker.
Also: Heart rate, measured every 5 minutes through the day and the night: all of it, not resting heart rate alone.
COROS's Daily Stress names 1 of the six inputs, HRV, and others beyond them. COROS calls heart rate and HRV its "two main data inputs" and says your own baseline settles after about a week. It publishes no formula.
Source: Daily Stress (COROS Support)
- HRV : not named Not named by the maker.
- Resting heart rate : not named Not named by the maker.
- Breathing rate : not named Not named by the maker.
- Sleep : not named Not named by the maker.
- Temperature : not named Not named by the maker.
- Activity or load : named by the maker Training Load, from the duration and intensity of recent workouts, and the energy left since your last exercise.
Also: Base Fitness, which COROS also works out from the duration and intensity of your workouts.
COROS's Recovery names 1 of the six inputs, activity or load, and others beyond them. COROS says sleep, HRV and Daily Stress "are not part of the Recovery calculation".
A list of scores, one per device, with six inputs for each: HRV, resting heart rate, breathing rate, sleep, temperature and activity or load. COROS's Daily Stress names 1 of the six inputs, HRV, and others beyond them. COROS calls heart rate and HRV its "two main data inputs" and says your own baseline settles after about a week. It publishes no formula. COROS's Recovery names 1 of the six inputs, activity or load, and others beyond them. COROS says sleep, HRV and Daily Stress "are not part of the Recovery calculation".
The Sleep Score weighs six factors, one of them sleep stress, which COROS ties to “elevated heart rate and lower overnight HRV” (COROS Support, Sleep Score). Recovery scores explained compares other makers’ scores.
Where to find HRV on COROS
- On the watch. Scroll down from the watch face through the widgets to Overnight HRV and press the dial to expand it. Scroll on for your 7-day summary (COROS Support, Overnight HRV).
- In the COROS app. Open the Progress page, choose Overnight HRV, and switch between Day, Week and Month for the trend.
- Wellness Check results appear on the watch straight after the test and sync to the app, where you can compare them with earlier checks (COROS Support, Wellness Check).
COROS lists Overnight HRV for the PACE 2, PACE 3, PACE 4, PACE Pro, NOMAD, APEX Pro 1, APEX 2, APEX 2 Pro, APEX 4, VERTIX 1, VERTIX 2 and VERTIX 2S, and the PACE 4 Pro’s setup guide includes it too (COROS Support, Overnight HRV; PACE 4 Pro). The original APEX 42mm and 46mm and the PACE 1 do not measure it (COROS, What is HRV?). Where do I find HRV on my device has the same steps for other brands.
Cost and getting your data out
COROS’s help pages for Overnight HRV, the Wellness Check and Daily Stress mention no subscription, and COROS describes its web Training Hub as free (COROS, Training Hub).
Getting the HRV numbers out takes more effort than getting workouts out:
- Workouts export in bulk from the Training Hub as .FIT or .TCX files.
- Sleep and daily data come by request: in the app, go to Profile, Customer Support, Contact Support, and give the date range you want. COROS lists daily metrics, sleep and heart rate under this route but does not name HRV (COROS Support, Bulk Export).
- Apple Health receives heart rate, sleep, steps and distances from COROS. HRV is not on the list (COROS Support, Apple Health).
- AI assistants can read daily HRV, stress and Wellness Check results through COROS’s connector, as of its September 2026 update (COROS Support, Connect Your COROS to AI).
How accurate is COROS HRV?
We searched PubMed and Europe PMC on 22 October 2026 and found no peer-reviewed study that compared a COROS watch’s HRV with an ECG or a validated chest strap. The device validation tracker has no COROS row. COROS’s own article says overnight and morning measurements “have been shown to be highly consistent with each other” and cites no study for it (COROS, What is HRV?).
Peer-reviewed HRV studies per brand in our tracker
Validation tracker
COROS has no row: we found no peer-reviewed study that compared its HRV with an ECG or a chest strap. A study counts once per brand, however many of the brand’s devices it tested.
Every study, with its numbers, is in the device validation tracker.
A list of brands, the most studied first, each with one square per study in the device validation tracker, filled for studies that tested the device overnight. Oura: 5 studies, 4 of them overnight. WHOOP: 3 studies, 3 of them overnight. Apple: 3 studies, 1 of them overnight. Garmin: 3 studies, 1 of them overnight. Polar: 1 study, 1 of them overnight. Samsung: 1 study, 1 of them overnight. Fitbit: 1 study, 1 of them overnight. RingConn: 1 study, 0 of them overnight. COROS: no study in our tracker. COROS has no row: we found no peer-reviewed study that compared its HRV with an ECG or a chest strap. A study counts once per brand, however many of the brand’s devices it tested.
The nearest evidence comes from other brands’ wrist devices. In a 2025 study of 13 healthy adults over 536 nights at home, with a chest-strap ECG as the reference, WHOOP 4.0 reached a concordance of 0.94 for overnight RMSSD, the Garmin Fenix 6 0.87 with an average error of 10.52%, and the Polar Grit X Pro 0.82; the authors rated the two watches’ agreement as poor (Dial and colleagues, 2025). Each maker’s sensor and software differ, so those results do not carry over to COROS. They show how far a wrist number can sit from the reference on a given night. Is wrist HRV as accurate as a chest strap? covers the general case.
How to read COROS HRV
- Read the week, not the night. With no published error figure for COROS, you cannot tell how much of a one-night change comes from the watch. Two or three nights below your range say more than one.
- Look for a reason. COROS lists hard exercise, large meals, alcohol and caffeine before bed as sources of sleep stress, which comes with lower overnight HRV (COROS Support, Sleep Score). Its list for a lower night also includes sickness and a poor night’s sleep.
- Keep Wellness Checks apart. A one-minute reading in bed and a whole-night average measure different stretches of time.
- Keep conditions the same. Same wrist, same fit, worn every night. A new watch or a firmware update can shift your values; see can a software update change my HRV.
- Compare COROS only with itself. Other brands average different parts of the night. HRV by device lists what each one measures, and normal HRV explains what published values can tell you.
For other brands, see Garmin HRV Status and Polar.
When to talk to a doctor
COROS says its HRV values “are for reference only and cannot diagnose any medical conditions” (COROS, What is HRV?). Talk to a doctor if low HRV or a run of nights below your range comes with feeling unwell, lasting fatigue, palpitations, dizziness, fainting or chest pain, whatever the number says.