How your stress score works
A transparent look at the science behind your 0-100 score. No black boxes.
One number, updated throughout the day
Your stress score is a number from 0 (completely calm) to 100 (extreme stress). It updates throughout the day as your wearable sends new biometric data. Think of it as a weather report for your nervous system: not a diagnosis, but a useful signal.
How data becomes your score
Four stages, from raw biometrics to a single number you can act on.
Biometrics
HRV, heart rate, sleep, activity from your wearable
Scoring Engine
Compares against your personal baseline
Context
Time, location, activity, calendar, weather
Your Score
0-100, personal, updated in real time
Biometrics
HRV, heart rate, sleep, activity from your wearable
Scoring Engine
Compares against your personal baseline
Context
Time, location, activity, calendar, weather
Your Score
0-100, personal, updated in real time
Biometric signals
Core input layer
Heart rate variability, resting heart rate, sleep quality, activity levels, and respiratory patterns feed into the scoring engine. HRV is one of more than 20 parameters, not the only one. Sereno uses Pearson correlation analysis to weigh each signal against your personal history, giving each parameter the influence it deserves for your body.
Behavioral and context signals
Equal-weight input layer
Location, time of day, physical activity, calendar events, weather, screen time, and sleep patterns carry equal analytical weight. A high heart rate during a morning run is normal. The same heart rate during a 3pm meeting tells a different story. These signals are not secondary modifiers. They are core inputs that the Pearson correlation engine evaluates alongside biometrics.
Your personal baseline
Adaptive learning
Sereno learns YOUR normal over 7-14 days. An HRV of 45ms might be stressed for one person but perfectly calm for another. Your score is personal. It reflects your body, your rhythms, your life. Not a one-size-fits-all formula.
The more you wear, the smarter it gets
Your baseline starts forming from day one. After 7 days, your score accuracy improves significantly as Sereno learns your weekly patterns. After 14 days, seasonal and time-of-day patterns emerge. The longer you use Sereno, the more personal your score becomes.
Day 1
First reading: basic score from initial data
Day 7
Weekly patterns: day-of-week accuracy improves
Day 14
Full baseline: circadian and activity patterns established
Ongoing
Continuous learning: adapts as your life changes
Day 1
First reading: basic score from initial data
Day 7
Weekly patterns: day-of-week accuracy improves
Day 14
Full baseline: circadian and activity patterns established
Ongoing
Continuous learning: adapts as your life changes
What we don't do
Transparency means being honest about limitations too.
We don't diagnose medical conditions. Sereno is a wellness tool, not a medical device.
We don't share your health data. Your biometrics stay on your device and in your iCloud, never on our servers.
We don't use population averages that ignore your body. Your score is built from your data, your baseline, your context.
We don't hide behind 'proprietary AI'. You know what feeds your score: 20+ signals analyzed through Pearson correlation against your personal baseline.
Built on real research
Sereno's multi-signal approach draws from decades of research in stress physiology, behavioral science, and wearable biometrics. Here are some of the key studies behind our scoring methodology:
A meta-analysis in Neuroscience & Biobehavioral Reviews found that lower HRV is consistently associated with higher stress, anxiety, and poorer cardiovascular health. (Chalmers et al., 2014)
Research published in Frontiers in Public Health shows that HRV is a reliable, non-invasive marker of autonomic nervous system function, which controls your stress response. (Shaffer & Ginsberg, 2017)
Studies demonstrate that guided breathing exercises increase HRV within minutes, measurably reducing physiological stress markers. (Lehrer & Gevirtz, 2014)
For deeper dives into the research behind stress and HRV, visit our blog (coming soon).
