how your cortisol score works.
Your cortisol score estimates how far your body's strain signals (heart rate, HRV, sleep, breathing) sit from your own usual, using your Apple Watch. It isn't a lab test, and it doesn't measure cortisol or any hormone.
What goes in
Six signals your watch already records:
- Resting heart rate
- Heart rate while you're sitting still
- HRV during the day
- HRV overnight
- How long you slept
- Your breathing rate overnight
To know when not to trust a reading, we also check wrist temperature, blood oxygen, workouts, mindful sessions and heart-rhythm records in Apple Health.
About half the score comes from how your night and resting heart compare with your usual. The other half comes from what your watch picks up through the day while you sit still.
Compared with you, not with other people
We learn your usual for each signal from your last 4 weeks. If Apple Health already has a week of readings, you won't wait. Until then we lean on typical values for people like you, by age and sex.
A score of 40 means your signals are right at your usual. Higher means they've moved the way they often do under strain: a higher heart rate at rest, lower HRV, a shorter night. Illness, alcohol and hard training move them too.
| Band | Score | What it means |
|---|---|---|
| Low | under 30 | Calmer than your usual |
| Usual | 30–49 | Around your usual |
| Raised | 50–59 | Higher than your usual |
| High | 60 and up | Well above your usual |
Why it changes
Your night sets each morning's starting point. Readings during the day nudge it, and the nudges fade back within a few hours. A single reading moves it only a little, and so does any one hour of readings. It moves more when readings keep pointing the same way for a few hours.
Every point is accounted for
Tap your score to see how many points each signal adds or takes off. They add up to your number.
When we're less sure, we say so
A missing signal counts for less, and your score leans toward your usual instead of guessing high. You'll see "rough estimate" and what would help.
What throws it off
We set heart readings aside during and just after workouts and breathing sessions, so they don't read as stress.
Some things change heart signals more than stress does. We pause your score for AFib and pregnancy, hide the number by default if you take steroid medicine, and adjust for beta-blockers (tell us in Settings). If your overnight readings suggest you may be unwell, we dim it. We don't yet adjust for alcohol or your cycle, so a higher score after drinking or before your period may be them, not stress.
If you take steroid medicine, your score can't guide your dose. Don't change any medicine because of it; talk to your doctor.
What we've tested
In public research recordings made with a different wristband (not Apple Watch), the daytime part of the score was higher during short lab stress tasks than at rest for most participants (data: Hongn et al. 2025, PhysioNet). That shows the signals respond to acute stress. It doesn't show how well the score tracks everyday stress. Everyday stress moves these signals much less than lab stress. We haven't tested this score against cortisol.
What it can't do
It can't diagnose anything, and it isn't intended for medical use. Check with a doctor in addition to using Cortisol IQ, and before making any medical decision.