What is the difference between resting heart rate and sleeping heart rate?

Resting heart rate is the device's own estimate of the user's heart rate at rest, reported by the device as a distinct value. Sleeping heart rate is Sahha's average of raw heart rate samples during the hours the user was in bed. A device that reports raw heart rate but no resting estimate produces only the second.

What is the readiness resting heart rate factor compared against?

The user's own 30-day average, excluding the current day. The goal on the factor is that average, and the score falls as the day's value moves away from it in either direction, scaled by how much the user's resting heart rate normally varies.

Why do two users with the same resting heart rate get different readiness credit?

Because the factor is relative to each user's own baseline and variability. A value of 62 is unremarkable for a user who averages 60 and alarming for one who averages 48.

Heart rate | Sahha

What the heart rate biomarkers measure

Biomarker	What it is
`heart_rate_resting`	The day’s average of the device’s resting heart rate estimates
`heart_rate_sleep`	The average heart rate across the hours the user was in bed

Field	`heart_rate_resting`, `heart_rate_sleep`
Unit	Beats per minute
Reported	Daily average
Window	Midnight to midnight, profile local time
Wearable required	Yes
API	`GET /api/v1/profile/biomarker/{externalId}?categories=vitals` plus one `types` parameter per field and a date range
Webhook	`BiomarkerCreatedIntegrationEvent`. Entries update in place, upsert on `id`.

Data sources

Platform	Resting heart rate	Raw heart rate (for sleeping heart rate)
iOS, HealthKit	`restingHeartRate`, computed by Apple Watch once a day from quiet periods	`heartRate` samples from Apple Watch
Android, Health Connect	`RestingHeartRateRecord`, written by Samsung Health, Fitbit, Garmin Connect, Pixel Watch and other apps	`HeartRateRecord` samples from the same apps
Direct integrations	WHOOP and Oura report a nightly resting heart rate; Garmin reports a daily one	Provider-dependent
Phone only	None	None

Each vendor defines resting heart rate differently. Apple samples quiet moments through the day. Oura and WHOOP take the overnight low or average. The values are not interchangeable across devices.

How Sahha calculates heart rate

Pick one source for the day. Within the heart category, a source that reports resting heart rate outranks one that reports only raw heart rate. One source wins per day; values from different devices are never blended.
Resting heart rate is the average of that source’s resting heart rate samples with an end time inside the local day. Most devices write one per day, so the average is usually that single value.
Sleeping heart rate is built from raw heart rate samples. Each hour of the day in which the user was in bed for at least 45 minutes, according to sleep records, is averaged, and those hourly averages are averaged again. Hours before midnight belong to the previous calendar date.

Absence means the winning source supplied no samples of that kind that day.

Interpreting the value

Read it against the user’s own history. Resting heart rate varies far more between people than within one person. For a per-user benchmark use the heart_rate_resting comparison insight, which places the value against global, demographic, and personal-baseline groups and treats lower as better.

Sleeping heart rate is usually lower and steadier than resting. It excludes daytime stress, caffeine, and posture, so it moves less day to day and shows illness, alcohol, and late meals more clearly.

A night that spans midnight is split. The in-bed hour before midnight counts toward the earlier date. Sleeping heart rate for a date mostly reflects the early-morning hours.

Score factor. The Readiness Score carries a factor named resting_heart_rate, unit bpm, whose value is the day’s resting heart rate. Its goal is the user’s own 30-day average, excluding the current day. Credit is 1 at the average and falls in proportion to how far the day’s value sits from it, measured in multiples of the user’s own 30-day standard deviation, with a floor of 0.2. A user whose resting heart rate never varies has no standard deviation to scale by, and no factor until it does.

Trend. A resting_heart_rate trend is available on the factor score.

Comparison. A heart_rate_resting comparison is available on the raw value. None for sleeping heart rate.

Use cases

A “higher than your usual” flag. Compare today’s resting heart rate with the user’s own 30-day baseline from the comparison insight. A rise of several beats sustained over two or three days, with no change in training, is the classic early sign of illness or overreaching [1], and the readiness factor already encodes it.

GET /api/v1/profile/biomarker/{externalId}?categories=vitals&types=heart_rate_resting&types=heart_rate_sleep&startDateTime=2026-08-03&endDateTime=2026-09-02

A sleeping heart rate history. The seven-night line of sleeping heart rate is the single most legible recovery chart for users, and it needs only raw heart rate plus sleep records.

Limitations

Values differ by vendor. Do not compare resting heart rate across users on different devices, and expect a step change when a user switches.
Sleeping heart rate needs both heart rate samples and sleep records. A phone-estimated sleep window can supply the hours, but the heart rate still has to come from a worn device.
The 45-minute rule drops short in-bed hours. The hour the user went to bed or got up is often excluded.
Absence is not zero.

Heart rate variability for the other readiness vital
Sleep duration for the sleep records that define in-bed hours
Readiness Score explained for how the personal-baseline factors combine
Data dictionary in the developer docs

References

Radin JM, Wineinger NE, Topol EJ, Steinhubl SR. Harnessing wearable device data to improve state-level real-time surveillance of influenza-like illness in the USA: a population-based study. The Lancet Digital Health. 2020;2(2):e85-e93. https://doi.org/10.1016/S2589-7500(19)30222-5

Heart rate