No recovery 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 has published evidence that it predicts how you will perform or recover, and no maker publishes its formula. What has been tested is the HRV inside the scores: in a 2025 study of 536 nights against a chest-strap 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 , Oura’s overnight 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 had an average error of about 6%, WHOOP’s 8%, Garmin’s 11% and Polar’s 16%. Trust the nightly HRV and 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 as a trend, and let the score summarise them.
What each score is made of
Pick a score to see which inputs its maker names, in the maker’s words.
What is in a readiness score?
From the makers' own documentation
- HRV : named by the maker HRV Balance: "How has my HRV changed over the past few weeks?" (a two-week average against three months).
- Resting heart rate : named by the maker Resting Heart Rate: "Was my RHR substantially higher or lower than usual?"
- Breathing rate : not named Not named by the maker.
- Sleep : named by the maker Sleep, Sleep Balance, Sleep Regularity and Recovery Index (hours of sleep after the heart rate reached its low).
- Temperature : named by the maker Body Temperature: "Is my body temperature higher or substantially lower than usual?"
- Activity or load : named by the maker Previous Day Activity and Activity Balance (recent load).
Oura's Readiness Score names 5 of the six inputs: HRV, resting heart rate, sleep, temperature and activity or load. "The sum of these daily Readiness Contributors make up your Readiness Score." No weights are published.
- HRV : named by the maker Heart rate variability; the API field for it is named hrv_rmssd_milli.
- Resting heart rate : named by the maker Resting heart rate.
- Breathing rate : not named Not named by the maker.
- Sleep : not named Not named by the maker.
- Temperature : named by the maker Skin temperature, for WHOOP 4.0 and later.
- Activity or load : not named Not named by the maker.
Also: Blood oxygen (SpO2) on WHOOP 4.0 and later. Sleep and breathing rate are not named in the developer documentation.
WHOOP's Recovery names 3 of the six inputs: HRV, resting heart rate and temperature. WHOOP lists the measurements that "factored into the score" but not how they are combined.
- HRV : named by the maker HRV status (the seven-day average against your baseline range), and the stress history of the last 3 days, which itself comes from HRV.
- Resting heart rate : not named Not named by the maker.
- Breathing rate : not named Not named by the maker.
- Sleep : named by the maker Last night’s sleep score and the sleep history of the last 3 nights.
- Temperature : not named Not named by the maker.
- Activity or load : named by the maker Acute load (recent training) and recovery time.
Garmin's Training Readiness names 3 of the six inputs: HRV, sleep and activity or load. The manual lists the six factors. It does not say how they are weighted.
- HRV : named by the maker Heart rate variability.
- Resting heart rate : not named Not named by the maker.
- Breathing rate : not named Not named by the maker.
- Sleep : named by the maker Sleep quality: "Good sleep charges your Body Battery."
- Temperature : not named Not named by the maker.
- Activity or load : named by the maker Activity data: "Strenuous activity and high stress can cause your Body Battery to drain more quickly."
Also: Stress level, which Garmin derives from HRV while you are inactive. Food and caffeine have no effect.
Garmin's Body Battery names 3 of the six inputs: HRV, sleep and activity or load. The manual names the four inputs and nothing more.
- HRV : named by the maker "Your device analyzes your heart rate variability while you are inactive to determine your overall stress."
- 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.
Garmin's Stress level is HRV only: a rescaled HRV number, not a mix. HRV is the only named input. How it maps to 0–100 is not published.
Source: Heart Rate Variability and Stress Level (Garmin owner’s manual)
- HRV : named by the maker Heart rate variability (RMSSD) from roughly the first four hours of sleep.
- Resting heart rate : named by the maker Heart rate over the same window: "Heart rate has the biggest influence when forming the score."
- Breathing rate : named by the maker Breathing rate, "the smallest" influence.
- 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: A separate Sleep charge compares the sleep score with your usual level.
Polar's Nightly Recharge (ANS charge) names 3 of the six inputs: HRV, resting heart rate and breathing rate. Polar ranks the three inputs by influence but does not give the weights.
Source: Nightly Recharge recovery measurement (Polar Support)
- HRV : named by the maker Heart rate variability.
- Resting heart rate : named by the maker Resting heart rate.
- Breathing rate : not named Not named by the maker.
- Sleep : named by the maker Sleep.
- Temperature : not named Not named by the maker.
- Activity or load : not named Not named by the maker.
Also: Activity was an input in the earlier version and is not in the updated algorithm.
Fitbit's Daily Readiness Score names 3 of the six inputs: HRV, resting heart rate and sleep. Google names the three inputs and does not publish the formula.
- HRV : named by the maker Heart rate variability.
- Resting heart rate : named by the maker Sleeping heart rate.
- Breathing rate : not named Not named by the maker.
- Sleep : named by the maker Sleep time average, sleep time consistency, bed and wake time consistency, and sleep timing.
- Temperature : not named Not named by the maker.
- Activity or load : named by the maker Previous day activity.
Samsung's Energy Score names 4 of the six inputs: HRV, resting heart rate, sleep and activity or load. Samsung lists the metrics the score combines and nothing about their weights.
- HRV : named by the maker HRV Form: your HRV baseline and how far last night departs from it; also the Stress Rhythm Score, which tracks heart rate and HRV across the day.
- Resting heart rate : named by the maker Overnight resting heart rate against your own baseline.
- Breathing rate : not named Not named by the maker.
- Sleep : named by the maker Sleep Index: length, efficiency, stage split and timing.
- Temperature : named by the maker Skin temperature against your usual overnight level.
- Activity or load : not named Not named by the maker.
Ultrahuman's Recovery Score names 4 of the six inputs: HRV, resting heart rate, sleep and temperature. "Each is graded on its own; then the five combine into the 0 to 100 score." No weights are published.
Source: Recovery Score (Ultrahuman)
- HRV : named by the maker Vitals, including Recovery HRV analysed against your personal baseline.
- Resting heart rate : not named Not named by the maker.
- Breathing rate : not named Not named by the maker.
- Sleep : named by the maker Sleep score.
- Temperature : not named Not named by the maker.
- Activity or load : named by the maker Recent activity and training load.
Also: Vitals also cover heart rate, breathing rate and wrist temperature; Apple does not say how each counts.
Apple's Readiness names 3 of the six inputs: HRV, sleep and activity or load. Apple names four inputs and publishes no formula. It has not said which statistic Recovery HRV uses.
- HRV : named by the maker RMSSD from a chest strap or finger sensor reading, with "a natural log (ln) applied".
- 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.
Elite HRV's HRV Score is HRV only: a rescaled HRV number, not a mix. The score is a rescaled ln(RMSSD), set so that "everyone fits in a 0 to 100 range" using over 6 million readings. The exact mapping is not given.
- HRV : named by the maker "Calculated from lnRMSSD."
- 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.
Welltory's HRV Score is HRV only: a rescaled HRV number, not a mix. Welltory names lnRMSSD as the input and publishes no formula or thresholds.
With JavaScript off, every score is listed below the menu.
A list of scores, one per device, with six inputs for each: HRV, resting heart rate, breathing rate, sleep, temperature and activity or load. Oura's Readiness Score names 5 of the six inputs: HRV, resting heart rate, sleep, temperature and activity or load. "The sum of these daily Readiness Contributors make up your Readiness Score." No weights are published. WHOOP's Recovery names 3 of the six inputs: HRV, resting heart rate and temperature. WHOOP lists the measurements that "factored into the score" but not how they are combined. Garmin's Training Readiness names 3 of the six inputs: HRV, sleep and activity or load. The manual lists the six factors. It does not say how they are weighted. Garmin's Body Battery names 3 of the six inputs: HRV, sleep and activity or load. The manual names the four inputs and nothing more. Garmin's Stress level is HRV only: a rescaled HRV number, not a mix. HRV is the only named input. How it maps to 0–100 is not published. Polar's Nightly Recharge (ANS charge) names 3 of the six inputs: HRV, resting heart rate and breathing rate. Polar ranks the three inputs by influence but does not give the weights. Fitbit's Daily Readiness Score names 3 of the six inputs: HRV, resting heart rate and sleep. Google names the three inputs and does not publish the formula. Samsung's Energy Score names 4 of the six inputs: HRV, resting heart rate, sleep and activity or load. Samsung lists the metrics the score combines and nothing about their weights. Ultrahuman's Recovery Score names 4 of the six inputs: HRV, resting heart rate, sleep and temperature. "Each is graded on its own; then the five combine into the 0 to 100 score." No weights are published. Apple's Readiness names 3 of the six inputs: HRV, sleep and activity or load. Apple names four inputs and publishes no formula. It has not said which statistic Recovery HRV uses. Elite HRV's HRV Score is HRV only: a rescaled HRV number, not a mix. The score is a rescaled ln(RMSSD), set so that "everyone fits in a 0 to 100 range" using over 6 million readings. The exact mapping is not given. Welltory's HRV Score is HRV only: a rescaled HRV number, not a mix. Welltory names lnRMSSD as the input and publishes no formula or thresholds.
Three patterns stand out. Every score uses HRV. Most add resting heart rate and sleep; some add temperature, breathing rate Breathing rate How many breaths you take a minute. It moves HRV on its own: slower, deeper breathing makes the beat-to-beat swing larger, and below about 9 breaths a minute it shifts from the HF band into LF. More about Breathing rate or activity. And every maker stops at the list: Oura says the sum of the contributors makes up Readiness, Garmin lists six factors for Training Readiness, Polar ranks heart rate above HRV above breathing rate, and none gives the weights. Two devices on the same wrist can therefore give different scores from the same night without either being wrong. The full write-up is in recovery scores explained.
What has been validated and what has not
The measurement underneath has been checked. Dial and colleagues had 13 healthy adults wear five devices and an ECG for 536 nights. For overnight RMSSD the concordance with the ECG was 0.99 for Oura Gen 4, 0.97 for Gen 3, 0.94 for WHOOP 4.0, 0.87 for the Garmin Fenix 6 and 0.82 for the Polar Grit X Pro. The authors rated Oura’s agreement highest, WHOOP’s acceptable, and Garmin’s and Polar’s poor. The study was small and its people were healthy, so it ranks these models on these nights, not every device for everyone.
The scores themselves have no such test in the makers’ documentation: no paper showing that a readiness of 85 predicts a better session than a readiness of 60 for the person wearing the device. The HRV by device guide has the full accuracy table.
Why a score can disagree with how you feel
- It leans on HRV, and HRV is not always honest. In Le Meur and colleagues’ study, 13 triathletes who did three weeks of overload training lost about 9% of their running performance while their weekly HRV rose. A score built on HRV would have looked good. Why your HRV is good but you feel tired covers this.
- Other inputs pull the other way. A short night with a high HRV can score low on one device and high on another, depending on how much sleep counts.
- Baselines differ. Oura compares two weeks with three months, Garmin seven days with three weeks, Polar one night with 28 days, Fitbit against a 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 from seven nights. A device with a longer memory reacts more slowly.
How to use a score well
- Open the nightly HRV and resting heart rate behind the score. Those are measurements; the score is an opinion about them.
- Look at the 7-day trend. The lesson on building your HRV baseline shows how.
- Read the score as a summary. If it agrees with the trend and with how you feel, act on it. If it disagrees, find the input that drove it.
- Keep one device for decisions. Comparing two scores day to day teaches you about the formulas, not about your body. Should I train when my HRV is low? gives a simple rule for the morning decision.
When to talk to a doctor
No score can diagnose illness or overtraining. Talk to a doctor if low scores come with feeling unwell, unusual fatigue that lasts, palpitations, dizziness or chest pain.