Stress score: how wearables measure stress from HRV

A stress score is a wearable's estimate of how much physiological load your body is under, based mainly on heart rate and heart rate variability (HRV) compared with your own baseline. Garmin, for example, scores stress from 0 to 100, where 0 to 25 is rest and 76 to 100 is high stress. A stress score measures body stress from any source, including exercise, alcohol, illness and poor sleep, not just emotions.

This article explains how stress scores work, how major devices present them, what the science on HRV and stress supports, and the limits you should keep in mind.

What is a stress score?

A stress score is a number that summarizes how activated your autonomic nervous system appears, estimated from heart rate and HRV. When the sympathetic ("fight or flight") side dominates, heart rate tends to rise and HRV tends to fall. Most devices compare current readings with your personal baseline and convert the difference to a scale.

Heart rate variability is the variation in time between heartbeats. Higher variability at rest is generally associated with more parasympathetic ("rest and digest") activity. For the basics, read what is a good HRV.

How do wearables measure stress?

Wearables measure stress by tracking HRV and heart rate while you are still and comparing them with your usual values. Garmin analyzes HRV while you are inactive. Oura combines heart rate, HRV, motion and body temperature during the day. Movement data helps separate exercise from other stress, which is why most readings are taken at rest.

Device	Scale	Inputs named by the maker	Notes
Garmin	0 to 100 (0 to 25 rest, 26 to 50 low, 51 to 75 medium, 76 to 100 high)	HRV while inactive	Training, activity, sleep, nutrition and life stress all affect it; best results when worn during sleep
Oura (Daytime Stress)	States such as Stressed, Engaged, Relaxed, Restored	Heart rate, HRV, motion, body temperature	Tracks when you are awake and fairly still
Apple Watch	No stress score described in Apple's guide	Not applicable	State of Mind logging in Mindfulness; Vitals app for overnight metrics

Sources: Garmin owner's manual; Oura blog; Apple Watch User Guide and Apple Support, as of October 2026.

What does the research say about HRV and stress?

Studies generally link psychological stress to lower parasympathetic activity in HRV. A 2018 review of 37 studies found the most common pattern under stress was lower high-frequency HRV and higher low-frequency HRV. Results varied between studies, and the authors described HRV as a marker of general autonomic function, not of a specific mental state.

Key points from Kim et al. (2018):

• Stress was most often associated with reduced high-frequency (parasympathetic) power and increased low-frequency power.
• Findings for individual measures were inconsistent across studies.
• Age, posture, breathing, lifestyle and medications all affect HRV.
• The authors recommended interpreting HRV alongside history and self-reports.

So a stress score is a reasonable signal that your body is under load. It is not a measure of how anxious or worried you are.

Why does my stress score go up when I do not feel stressed?

Your body does not separate physical and psychological stressors, so a stress score rises with anything that activates the nervous system. Oura gives the example of alcohol raising heart rate while you relax with a drink. Digestion, a recent workout, illness, heat and short sleep can all raise readings without any feeling of stress.

Common cause of a high reading	Why it registers
Alcohol	Oura notes it can raise heart rate even while you relax
Recent hard exercise	Recovery keeps heart rate elevated
Short or poor sleep	Can leave the body under more load the next day
Illness or fever	Raises heart rate
Caffeine	Stimulant; effects vary by person
Emotional stress	Sympathetic activation

Treat the table as a list of things to rule out, not a diagnosis. For how drinks show up overnight, see alcohol and HRV.

Does sleep affect your stress score?

Often, yes. Sleep is part of the load your body carries, and some stress scores, including the one described below, use sleep debt as a direct input. Sleep loss also builds quietly: in a 14-day lab study, people sleeping 6 hours a night kept getting worse on attention tests while rating themselves only slightly sleepier.

Stress and sleep often move together. If your stress score has been high for a week, check your sleep score and sleep debt before anything else.

Is a high stress score bad?

A high stress score is not bad on its own. Short spikes during exercise, a busy meeting or a hot day are normal responses. Garmin notes that training, physical activity, sleep, nutrition and general life stress all affect its reading. What matters more is the balance across a day: periods of activation followed by periods of rest and recovery.

Oura makes a similar point. It notes that members may spend more time in a Stressed state than a Restored state, and that this alone is no reason to assume the worst. The useful signal is a pattern that lasts: several days with little time at rest, often alongside short sleep or feeling run down.

Pattern	Likely reading
Brief spikes, low readings overnight	Normal daily ups and downs
High in the evening after drinks or a late meal	Body still processing; check sleep that night
High most of the day for several days	Worth looking at sleep, training load and illness

How can I measure stress without a wearable?

You can measure stress without a wearable by rating it yourself. Researchers often pair HRV with self-report questionnaires, and the 2018 review recommended reading HRV alongside self-reports and history. A simple daily rating of mood and stress, logged at the same time each day, gives you a trend to compare with sleep and activity.

On Apple Watch, the Mindfulness app lets you log your state of mind as a momentary emotion or as your overall mood for the day. You can then view entries in the Health app on iPhone. A self-rating captures how stress feels, which a heart rate signal can not.

How should I use a stress score?

Use a stress score to spot patterns, not to judge single readings. Look for repeated spikes at the same time of day, after the same activities, or after poor nights. Then test changes: earlier bedtime, less alcohol, a short walk or slow breathing. Compare your own week-to-week averages, not your number with someone else's.

If you feel persistently anxious, low or overwhelmed, or if stress is affecting your sleep, work or relationships, talk to a doctor or mental health professional. A wearable can not diagnose anxiety, depression or any other condition.

How Svanu calculates its stress score

Svanu computes a stress score from 0 to 100 on your iPhone, where a higher score means more load. It uses your resting heart rate and sleep debt and, when you wear an Apple Watch during the day, daytime HRV. Like every score in the app, it shows its inputs and what moved it.

The stress score also feeds the daily check-in and day score, together with your mood, bedtime consistency and strain versus target. There is no account and no health database on a server. See how the app works or read what is a good HRV for the HRV side.

Related reading

• Sleep score: what it measures and what a good score is
• Sleep debt: how to calculate it and pay it back
• What is a good HRV?
• Alcohol and HRV