Why HRV apps show different numbers on Apple Watch

First, check the metric and its units

A value such as 45 milliseconds describes an HRV measurement. A recovery result of 75% describes an app's interpretation of data. Comparing the two will not tell you whether either calculation is wrong.

Even two values in milliseconds can represent different measures:

• SDNN describes the spread of normal heartbeat intervals around their mean.
• RMSSD calculates the root mean square of the differences between consecutive normal heartbeat intervals.

The formulas use different information from the interval sequence, so matching units do not make the results interchangeable. A study of 3,387 adults also found that the agreement between short and longer ECG recordings depended on the metric and recording length. That study examined ECG recordings, not the relative accuracy of these apps.

Apple now distinguishes Recovery HRV from overall HRV on supported watches. Its September 2026 announcement describes both. Check the full label rather than assuming that every HRV chart in Health represents the same measure. Our HRV metrics guide explains the individual calculations.

A morning reading and an overnight average answer different questions

One app might show your latest reading. Another might average measurements taken during sleep. A third may use a planned morning session. The watch can supply data to all three while each app selects a different part of it.

Consider a simple example: three overnight readings are 30, 40 and 50 ms. Their arithmetic mean is 40 ms. A later morning reading is 60 ms. A screen showing the overnight mean and a screen showing the morning result will differ by 20 ms, even when both reproduce their selected data correctly. These are illustrative values, not an expected pattern or a healthy range.

Check whether a displayed average covers sleep, a calendar day or a selected session. For overnight data, also compare the sleep start and end times. A late-arriving sleep record can change which measurements fall inside the selected window.

Sampling frequency varies with the watch and recording conditions. More readings can give an app more data to select from, but they do not make its selection identical to another app's. See how often Apple Watch records HRV if the timestamps themselves look unexpected.

What to check in Bevel, Athlytic and other HRV apps

These are documented differences to investigate, not instructions to change every setting. Settings can vary with your app version and watch model.

Bevel documents RMSSD as its default and supports different measurement windows. Athlytic can also use RMSSD or SDNN; on Series 12 and Ultra 4, its documentation describes a switch to Apple's Recovery HRV after 14 days of that data. A watch upgrade can therefore change the input used by an app. Recheck the method when comparing results from before and after an upgrade.

The name Recovery HRV needs particular care in Wellhero. It names the HRV value selected for Wellhero's recovery assessment and currently uses SDNN. It should not be assumed to match Apple's separately named Recovery HRV metric.

Filtering and syncing can change what reaches the screen

Sharing a data source does not guarantee identical processing. Bevel's common questions describe filtering noisy readings. Athlytic says it filters beat-interval artifacts when calculating its own RMSSD, while its SDNN option uses Apple's supplied value without adjustment. An average calculated after excluding samples can differ from one that includes them.

This is a reason to inspect the inputs, not proof that the app with a higher or lower number is more accurate. The displayed result alone cannot show which samples were retained or how a filter behaved.

A phone app and its watch complication may also display results from different update times. Athlytic warns that widgets and complications can take time to reflect a changed HRV method. StressWatch's update notes distinguish stress estimates from HRV recordings and watch-face refreshes. Open the full app and compare timestamps before treating a stale complication as a calculation mismatch.

Why recovery scores can disagree even when HRV matches

Recovery scores have app-specific inputs and scales. Athlytic's getting-started guide describes a 0 to 100% score that compares HRV and resting heart rate with a rolling 60-day baseline. Bevel lists Sleep Score, HRV, resting heart rate and sufficient baseline data among its recovery requirements. Wellhero compares available HRV and resting heart rate with your own history.

A shared percentage scale does not establish a common formula. If two apps both show 70%, you cannot conclude that they agree about every input. If one shows 70% and the other 85%, the difference is not a measured 15-point error.

A current stress estimate also need not agree with a daily recovery assessment. StressWatch describes its stress interpretation in terms of HRV and resting heart rate; Wellhero separates an individual stress report from daily recovery. Compare each result with the same type of result in its own history.

How to investigate different HRV readings

1. Write down the full metric name, units, date and time from both screens. Distinguish a measurement from an average or score.
2. Open the HRV category in Apple Health and inspect Show All Data. Check the individual records and Data Sources & Access. Apple's Health data guide explains these controls; navigation labels can vary by iOS version.
3. Check each app's formula and time window using the links above. Compare the same session or night where possible.
4. If a reading exists in Health but is missing from one app, review the relevant Health permissions and allow syncing to finish. If Health has no reading for that period, start with the watch's recording history.
5. Save screenshots of the results and settings if the difference remains unexplained. Give the app's support team the metric, source and timestamps so they can investigate that specific calculation.

Keep the original Health records while investigating. Deleting samples to make a chart look consistent can remove data that other apps need. Athlytic specifically warns that deleting an SDNN sample also removes the underlying beat-to-beat data it uses for RMSSD.

Once you understand the inputs, keep the measurement routine and settings consistent when following trends. Record any method change so a break in the chart is not mistaken for a change in your body.

Check the readings behind your Wellhero score

In Wellhero, open Recovery to see the HRV and resting heart rate values used for the daily assessment and their history. If you also took a separate measurement, compare its timestamp and metric with the selected Recovery HRV before expecting them to match.

The Apple Watch setup guide covers importing readings and planned measurements. If you are choosing an app, our Apple Watch HRV and stress app comparison explains the different workflows. You can download Wellhero to explore your own recorded data.

Wellhero's recovery estimate is a wellness tool, not a diagnosis. A reassuring score should not be used to dismiss symptoms or replace medical care.