In one sentence
Two ways of asking how stressed you are: a four-question scale that measures how unpredictable, uncontrollable and overloaded your life has felt, and a single 0-to-10 question for today.
Why it matters
Stress is the thing people most want their wearable to measure and the thing it measures worst. HRV responds to stress, but it responds to everything else as well: in 9 million readings it proved a sensitive but not a specific marker, moving for training, alcohol, the menstrual cycle and being unwell as readily as for a hard week (Altini 2021). So VT asks. The Perceived Stress Scale (Cohen 1983) is the most widely used instrument for the feeling itself, and it measures appraisal rather than events: not what happened, but how far it felt beyond your control. The four-item version keeps two items that run each way. VT asks the four items daily, about today: today I felt unable to control the important things in my life; confident about my ability to handle personal problems (reverse-scored); that things were going my way (reverse-scored); that difficulties were piling up so high I could not overcome them. Each 0 (never) to 4 (very often), for a total of 0 to 16. The daily question is simpler: how stressed are you today, 0 to 10.
What moves it
Life. Also sleep, which lowers the threshold at which everything feels like too much; being unwell; and the hour you answer.
How to answer it well
Both ask about today, so answer them late in the day. VT counts a day as a high-stress day when the PSS-4 total is 8 or more or the daily answer is 5 or more, and counts those days on the stress panel.
How Vitality Tracker uses it
The PSS-4 total feeds the recovery side of Capacity, compared with your own usual, alongside fatigue and vigor; on a day without it, the daily question stands in. Both count toward high-stress days, and both sit in your record beside the overnight readings, so that you can see what a stressful stretch does to your heart rate and HRV. Neither is a Symptom Radar reading, and neither is scored anywhere else.
How far to trust the number
Self-reported, and designed for within-person comparison. It is a measure of how you feel, not a diagnosis of anything; if the number stays high for weeks, that is a conversation to have with someone, not a result.
Sources
- Cohen S, Kamarck T, Mermelstein R. A global measure of perceived stress. J Health Soc Behav 1983;24:385–96 (PMID 6668417)
- Altini M, Plews D. What is behind changes in resting heart rate and heart rate variability? Sensors 2021;21:7932. doi:10.3390/s21237932
- Vitality Tracker, What VT measures (catalogue of 15 October 2026).