Amazfit is Zepp Health’s watch brand, and its devices all report to one phone app, Zepp. The current line runs from the Bip, Active, Balance, Cheetah and T-Rex watches to two screenless trackers, the Helio Strap and Helio Strap Pro. All of them use Amazfit’s BioTracker optical sensor, and Amazfit documents HRV the same way across them, so this guide covers the brand as a whole.
Documentation checked: 22 October 2026. Amazfit has changed its daily score more than once, so menus and names may have moved since.
What HRV number Amazfit shows
Amazfit’s product pages list “sleep heart rate variability” among the sleep metrics of the Balance 3, Active 3 Premium, T-Rex 3 Pro, Bip 6, Helio Strap and Helio Strap Pro (Amazfit product pages). The Bip 6 page describes it as “the time between heartbeats while you sleep”. That is closer to a definition of the RR interval RR interval The time from one heartbeat to the next, measured in milliseconds between the R peaks of an ECG. HRV is calculated from a series of these intervals. More about RR interval than of HRV, which describes how much those gaps change from beat to beat (Task Force, 1996).
Amazfit does not say whether its number is RMSSD, 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 or something else, and it does not say whether it averages the whole night or a shorter window. Oura, WHOOP, Polar and Fitbit report 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 ; Garmin and Samsung, like Amazfit, do not state outright which statistic they show. So you cannot match an Amazfit value to published norms or to another brand’s number, even on the same night. RMSSD, SDNN and lnRMSSD explains why the statistic changes the size of the number.
The Helio Strap uses the same sensor family but is worn differently. Amazfit says it can go on the upper arm for training or on the wrist “for everyday health and recovery monitoring” (Amazfit, Helio Strap). Pick one place for sleep and keep it there, so your nights stay comparable.
When Amazfit measures HRV
Amazfit takes HRV from sleep, so wear the device in bed. The Balance 3 manual calls sleeping in the watch “strongly recommended for more accurate recovery analysis”. Two optional settings in the Sleep app record more: assisted sleep monitoring adds REM stages, and sleep breathing quality monitoring tracks your breathing (Amazfit, Balance 3 user manual).
Amazfit spells out which sleep counts. Sleep that overlaps your sleep schedule becomes the main sleep of the day; with no schedule set, the default window is midnight to 8:00. The device logs sleep more than 60 minutes away from the main sleep as a nap and ignores anything under 20 minutes (Amazfit, Helio Strap user manual). If your main sleep is by day, set a schedule for it under Sleep > Sleep Regularity > Sleep Schedule in the Zepp app; otherwise, Amazfit says, the device records that sleep as naps (Amazfit Support, daytime sleep). Do night shifts lower HRV covers what shift work itself does to the number.
The watches also use HRV during the day. The stress index Baevsky stress index A number built from the histogram of heartbeat intervals, with no unit. It rises as the rhythm gets steadier and less variable, which Baevsky read as strain on the body's regulation. More about Baevsky stress index “is calculated based on changes in heart rate variability”, and with automatic monitoring on, the watch measures it every five minutes (Amazfit, Balance 3 user manual).
BioTracker optical sensor
In Amazfit watches, the Helio Strap and the Helio Ring.
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Sleep HRV
Recorded while you sleep and shown in the Zepp app.
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Stress
Worked out from changes in HRV, every five minutes when automatic stress monitoring is on.
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HybridCharge
The morning Wake score combines HRV with sleep quality, resting heart rate and the previous day’s mental fatigue. Some devices still show BioCharge or Readiness.
Not published by Amazfit
- Which HRV statistic it reports (RMSSD, SDNN or another)
- Which part of the night it averages
- How much HRV counts in the score
A diagram. At the top, the optical BioTracker sensor in an Amazfit watch, the Helio Strap or the Helio Ring. Arrows lead to three uses of the heart rate variability it records: sleep HRV, shown in the Zepp app; stress, worked out from changes in HRV every five minutes when automatic stress monitoring is on; and the HybridCharge score, whose morning Wake score combines HRV with sleep quality, resting heart rate and the previous day’s mental fatigue. Below, a grey box lists what Amazfit does not publish: which HRV statistic it reports, which part of the night it uses, and how much HRV counts in the score.
HybridCharge, BioCharge and Readiness
Amazfit has three daily scores built partly on HRV, and the one you see depends on the device and its software. The Bip 6 and the Helio Ring show Readiness. Zepp’s technology page says it uses “sleep resting heart rate Resting heart rate How many times your heart beats per minute while you are fully at rest. For adults it is usually 60 to 100 beats per minute, and lower in well-trained athletes. More about Resting heart rate , sleep heart rate variability, breathing quality and body temperature”, and the Bip 6 manual adds stress and activity (Zepp Health, Technology; Amazfit, Bip 6 user manual). The Helio Ring’s help page says the ring produces a 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 at the end of the night’s sleep (Amazfit Support, Helio Ring). Amazfit’s US store did not list the ring on 22 October 2026.
BioCharge appeared on the Helio Strap and on watches such as the Active 3 Premium. It scores 0 to 100 from heart rate, stress, sleep, HRV, breathing quality and activity (Amazfit, Active 3 Premium user manual). The Helio Strap Pro manual adds that the morning value draws on nighttime sleep, HRV, resting heart rate and activity data from the past three days, and that for the first seven days the score leans on other users’ averages until it has 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 (Amazfit, Helio Strap Pro user manual).
HybridCharge is the current score. Zepp app version 10.4.1, released on 27 May 2026, “upgraded” BioCharge to it (Zepp, App Store version history). Zepp Health describes it as BioCharge, LifeLoad and Training Load combined “into one view of capacity” (Zepp Health, 2026). The Balance 3 manual lists heart rate, HRV, stress, sleep quality, activity levels and workout load, plus LifeLoad, on a 0–100 scale (Amazfit, Balance 3 user manual). LifeLoad is the new part: events you log yourself, such as poor sleep, an intense work day, travel fatigue or muscle soreness. The Wake score, given each morning, fuses “sleep quality, heart rate variability (HRV), and resting heart rate with the lingering mental fatigue from the previous day” (Amazfit Support, Wake HybridCharge).
What is in a readiness score?
From the makers' own documentation
- HRV : named by the maker Heart rate variability: the Wake score fuses it with sleep quality and resting heart rate.
- Resting heart rate : named by the maker Resting heart rate, in the Wake score.
- Breathing rate : not named Not named by the maker.
- Sleep : named by the maker Sleep quality.
- Temperature : not named Not named by the maker.
- Activity or load : named by the maker Activity levels and workout load.
Also: Stress, and LifeLoad events you log yourself, such as poor sleep, a hard work day, travel or sore muscles.
Amazfit's HybridCharge names 4 of the six inputs: HRV, resting heart rate, sleep and activity or load. Amazfit lists the inputs and does not publish the weights.
- HRV : named by the maker HRV; Zepp’s technology page says "sleep heart rate variability".
- Resting heart rate : named by the maker Heart rate; Zepp’s technology page says "sleep resting heart rate".
- Breathing rate : not named Not named by the maker.
- Sleep : named by the maker Sleep.
- Temperature : named by the maker Temperature.
- Activity or load : named by the maker Activity.
Also: Stress, and breathing quality during sleep.
Amazfit's Readiness names 5 of the six inputs: HRV, resting heart rate, sleep, temperature and activity or load. Amazfit lists the data it uses and publishes no formula.
A list of scores, one per device, with six inputs for each: HRV, resting heart rate, breathing rate, sleep, temperature and activity or load. Amazfit's HybridCharge names 4 of the six inputs: HRV, resting heart rate, sleep and activity or load. Amazfit lists the inputs and does not publish the weights. Amazfit's Readiness names 5 of the six inputs: HRV, resting heart rate, sleep, temperature and activity or load. Amazfit lists the data it uses and publishes no formula.
HRV is one input among many, and Amazfit publishes no weights, so a low HybridCharge does not tell you that your HRV fell. And because LifeLoad entries move the score, two people with the same night can get different numbers. Amazfit also says the watch may show an older score than the app until it syncs, and that the app’s figure is the current one (Amazfit Support, charge score). Recovery scores explained compares this kind of score across brands.
Where to find HRV in the Zepp app
- In the Zepp app. The Helio Strap manuals say you can view the heart rate curve, resting heart rate, heart rate variability and heart rate zones there once the device has synced (Amazfit, Helio Strap user manual). Opening the app with Bluetooth on syncs the device; pulling down on the main screen syncs it by hand (Amazfit Support, sync).
- On the watch. The HybridCharge app on the Balance 3, the BioCharge app on the Active 3 Premium and the Readiness app on the Bip 6 show the score, with seven days of history on the latter two. The Balance 3 manual does not list HRV among what the watch’s Heart Rate app shows.
- Helio Strap. It has no screen, so everything appears in the Zepp app.
Where do I find HRV on my device has the same steps for other brands.
Does Amazfit need a subscription?
Not for the numbers. The Zepp app’s listing says you won’t need to pay “to view data tracked by your Amazfit device” (Zepp, App Store), and Amazfit sells the Helio Strap and Helio Strap Pro with no required subscription (Amazfit, Helio Strap).
Zepp Aura is the paid layer. Its free tier has sleep music, guided meditation and one message a day to an AI sleep assistant; Premium adds unlimited chats, detailed weekly and monthly sleep reports and a larger audio library. On Amazfit’s US store on 22 October 2026, Premium cost $11.99 a month or $69.99 a year, after a 14-day free trial (Amazfit, Zepp Aura). Readiness Insights, the expert-written notes that come with the Readiness score, need a Zepp Aura subscription (Zepp Health, Technology), and the Helio Ring’s help page says the service runs only in select regions (Amazfit Support, Helio Ring). On these pages the paid part is the written analysis; the score and your HRV data stay free to view.
Exporting Amazfit HRV
Amazfit’s Balance 3 firmware notes for July 2026 list “support for syncing HRV data to Apple Health” (Amazfit, Balance 3). The Zepp app also syncs with Strava, TrainingPeaks, Runna, Google Fit and intervals.icu, but Amazfit does not say which of them receive HRV. Apple Health files HRV under a named statistic, so check which one arrives there before mixing it with readings from another device.
For a full copy of your data, Zepp’s privacy policy, effective 14 July 2026, says that, where the law provides it, you may “receive an electronic copy of personal information that you have provided”, requested through its Privacy Support portal (Zepp Health, Privacy Policy). In the manuals and help pages we checked, Amazfit describes no button that exports your HRV history as a file.
How accurate is Amazfit HRV?
We do not know, and Amazfit publishes no error figure. A search of Europe PMC and Crossref on 22 October 2026 found no peer-reviewed study comparing an Amazfit device’s HRV with an ECG 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 or a chest strap, and our device validation tracker holds none.
Peer-reviewed HRV studies per brand in our tracker
Validation tracker
Amazfit 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. Amazfit: no study in our tracker. Amazfit 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 studies we found that include Amazfit tested heart rate only. In one, 51 patients with ischaemic heart disease did an incremental treadmill test with a 12-lead ECG attached and Amazfit Cor and Bip trackers on the wrist. The trackers’ heart rate error stayed inside the accepted 10% range at every stage and was smallest at low intensity; the study did not measure HRV (Ibrahim and colleagues, 2024). HRV needs each beat timed to within milliseconds, so accurate heart rate does not guarantee accurate HRV.
The closest evidence comes from other brands’ watches. In a 2025 home study of 13 adults over 536 nights, the two watches tested, a Garmin Fenix 6 and a Polar Grit X Pro, were on average 10.52% and 16.32% off a chest-strap ECG, and the authors rated both as poor (Dial and colleagues, 2025). Amazfit may do better or worse; no one has published a measurement. Is wrist HRV as accurate as a chest strap covers why optical sensors drift from an ECG.
How to read Amazfit’s numbers
- Look at HRV before the score. HybridCharge mixes HRV with sleep, heart rate, activity, stress and your own entries. If the score drops, check whether HRV moved at all.
- Give it a week. The Helio Strap manuals say the charge score leans on other users’ averages for the first seven days. How long until my HRV baseline is reliable explains why longer is better.
- Read weeks, not nights. Don’t read much into a one-night change of around 10%. In the Dial study, the two watches were off the ECG by 10% or more on average, and Amazfit has no figure of its own.
- Keep conditions the same. Same wrist or arm, same tightness, sleep monitoring settings unchanged. A firmware update can shift the values; see can a software update change my HRV.
- Compare Amazfit only with itself. Its statistic and window are unpublished, so it will not match an Oura, WHOOP, Garmin or Polar number. HRV by device lists what each brand measures.
When to talk to a doctor
Amazfit states that its devices and the Zepp app “are not medical devices” and are not a basis for diagnosis (Amazfit, Helio Strap). Talk to a doctor if low HRV or a run of low scores comes with feeling unwell, lasting fatigue, palpitations, dizziness, fainting or chest pain, whatever the number says.