Your Smartwatch Actually Has No Idea How “stressed” You Are.

Garmin displays a real-time stress level from 0 to 100. Oura calculates ” daily stress ” and resilience scores. Whoop is a stress monitor ; Fitbit has a “stress management score.” Whatever it’s called, some version of a “stress score” has become ubiquitous on smartwatches and wearables. This number is positioned as an indicator of our internal emotional state, turning into quantitative evidence of how our day is actually going. The only problem: these numbers aren’t always accurate.

What does your “stress score” really show?

The metrics displayed on our wrists don’t measure what most of us think. When you check your smartwatch and see that your stress level has spiked, you might assume the device has somehow detected your anxiety triggered by some immediate stimulus, like a difficult conversation or a traffic jam. But that’s not quite true.

Sure, your watch might have detected physiological arousal—changes in heart rate variability, skin conductance, or movement patterns. And while these signals do tell us something about the nervous system, they don’t actually tell us about stress in the psychological sense that really matters.

“Part of the discrepancy stems from different definitions of how stress is conceptualized,” says Eiko Fried, co-author of a 2025 study that found that stress indicators measured by smartwatches don’t align with most people’s self-reported stress levels. The way most people understand the term “stress”—for example, ” I was really stressed today! “—doesn’t align with the definition of the stress score, which Garmin uses to measure physiological stress. So, your watch doesn’t necessarily indicate how stressed you are, only how your nervous system is behaving. “This increased activity can come from a variety of sources,” says Fried, “including many that we don’t typically consider stressful.”

Physiological arousal occurs in response to a wide variety of experiences that have nothing to do with stress. “What most smartwatches call a ‘stress indicator’ isn’t actually stress,” says Erwin van den Burg , a physiologist specializing in stress biology. “It’s typically based on indirect physiological signals, such as heart rate variability, skin conductance, or movement patterns. These signals tell us something about arousal in the nervous system, but arousal can come from many sources—physical activity, excitement, caffeine, poor sleep, illness, or emotional engagement—not just psychological stress.”

This oversimplification becomes even more problematic when you consider that most stress-assessment algorithms don’t take into account physiological differences specific to each gender, especially the menstrual cycle. Because hormonal fluctuations can significantly alter heart rate, heart rate variability, and temperature, “a perfectly healthy physiological change can be interpreted by a wearable device as ‘high stress,'” says Emil Radite , CEO of Samphire Neuroscience. This means women are more likely to receive misleading stress alerts that don’t align with standard human biological markers, which can be confusing at best and alarming at worst.

Can you even trust your “stress score”?

Even if we put aside the definitional problem and the issue of gender bias, the fundamental question of measurement accuracy remains.

“If you have heart problems, your cardiologist may ask you to wear a chest strap for a few days to monitor your heart rate and heart rate variability. This is a highly accurate medical device,” says Fried. “Your doctor won’t ask you to wear a smartwatch because there are many issues that make wrist-based measurements less reliable. This particularly affects heart rate variability, for which we require highly accurate measurements.”

Heart rate variability is the cornerstone of most stress indicators measured by smartwatches, but wristwatches struggle to measure it with the accuracy needed for medical data. The data isn’t useless, but it’s noisy, and drawing definitive conclusions about your internal state from it is, to put it mildly, scientifically questionable.

So, are your wearables useless? Of course not. My criticism here isn’t that wearables are worthless, but that their value is being distorted. Your smartwatch’s “stress score” supposedly tells you far more than scientific evidence supports. And in some cases, a less-than-perfect score can actually increase stress levels, rather than helping people understand how their bodies are responding. The great irony of the wellness industry persists.

Result

Your perception of “stress” isn’t reducible to any single biological state, much less one that can be measured with a number or a “score.” Your clock simply records signs of arousal in your nervous system, which could mean almost anything.

This distinction doesn’t render the data useless, but it should make you a more informed consumer. It would be nice if companies stopped using the word “stress” to describe what they’re actually measuring—perhaps “physiological arousal” or “autonomic nervous system activity,” which would be more accurate but less marketable, so I don’t hold out much hope. (Although, if I did, my stress score would skyrocket.)

A device marketed as a stress management tool can actually exacerbate it by generating alarming signals of normal physiological fluctuations that it mistakenly interprets as stress. The sooner we honestly acknowledge this disconnect, the sooner these devices can help us, rather than selling us an illusion of self-knowledge they don’t actually provide.

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