What Is The Difference Between Wearable Sleep Scores & Clinical Sleep Test Results?
Sleep trackers have become a nightly ritual for a huge share of us, quietly logging every toss, turn, and moment of stillness. According to the American Academy of Sleep Medicine, nearly half of Americans adults1 have used some kind of sleep-tracking device. But new research suggests the numbers on your wrist might be telling a slightly rosier story than what's actually happening while you sleep.
What the study found
Researchers followed 107 patients at a sleep clinic over the course of eight nights. Each patient wore a MotionWatch 8 actigraphy device (a research-grade sleep tracker that measures movement) while simultaneously undergoing polysomnography, the gold-standard test that tracks brain waves, breathing, and eye movement to determine exactly when someone is asleep or awake.
The correlation between the two methods was strong when it came to total sleep time, meaning the tracker's overall ballpark wasn't wildly off. But when it came to more nuanced measures, like fragmented sleep or restlessness, the correlation was much weaker. Across the board, the wearable device didn't quite match what was happening in the sleep lab. Trackers overestimated total sleep time by an average of 27 minutes and overestimated sleep efficiency (the percentage of time in bed actually spent asleep) by about 6%. On the flip side, they underestimated time spent awake by about 15 minutes.
But overall, the research shows that the tracker might get the big picture close to right, but it struggles with the finer details of how choppy or smooth your night actually was.
What else affected sleep score?
The study found that accuracy wasn't uniform across all participants. Age played a role, with tracking accuracy shifting as participants got older. Periodic limb movements, a common issue in which the legs twitch or jerk during sleep, also affected how well the device's readings lined up with the lab results.
Setting also impacted sleep scores. The same device produced different results depending on whether someone was sleeping in the unfamiliar environment of a sleep lab versus their own bed at home. This is likely less of a problem with the device, but rather evidence that the where you are sleeping can shift the numbers you see. It's hard to compare a night in a hotel to a night in your own bedroom.
It's also worth noting that this study was conducted in a sleep clinic, meaning participants were already being evaluated for potential sleep issues, so results may not perfectly mirror what a healthy sleeper without sleep concerns would see.
How to use your tracker wisely
Based on this research, it appears a lot of us are checking a number each morning that likely skews a bit optimistic, especially when it comes to how much of the night was spent tossing and turning versus soundly asleep.
That's not a reason to give up on your tracker and toss it in a drawer. It's simply useful context for how much weight to give any single night's score. Because trackers can still be genuinely useful tools when you know their limits.
Here's how to get the most out of yours:
- Focus on trends, not single nights: One night's score can be thrown off by all kinds of normal variables, so there's no need to panic from one off night. Look at your data over a week or two to spot real, meaningful patterns in your sleep.
- Don't self-diagnose from the data: If your tracker shows frequent wake-ups or low sleep efficiency, resist the urge to assume you have a specific sleep disorder. These devices are movement-based estimates, not diagnostic tools. They're especially imprecise when it comes to fragmented sleep.
- Talk to a doctor about real concerns: If you consistently feel exhausted, struggle to fall asleep, or suspect something like sleep apnea or restless leg syndrome, see a sleep specialist rather than relying on wearable data alone. A clinical evaluation, potentially including a polysomnography test, can give you answers your tracker isn't built to provide.
- Use it as a nudge, not a verdict: If your tracker consistently shows short sleep windows or late bedtimes, treat that as a gentle prompt to adjust your routine, not as a definitive medical reading.
The takeaway
This study isn't saying your sleep tracker is lying to you—it's simply doing the best it can with the knowledge it has. The sleep tracker has an inherent bias toward the optimistic side of the numbers, particularly when it comes to how much of the night you were actually awake.
If you have been treating your sleep score as gospel, this is a sign that it may be time to give it a bit less energy. Rather than a diagnostic tool you take at face value, use your sleep data as a helpful nudge toward better sleep habits and a way to spot trends over time.
