Are Sleep Trackers Accurate?

Sleep trackers are good at estimating how long you slept and much weaker at everything else, including the part that matters most if you have insomnia.

One widely cited test put seven consumer devices up against polysomnography, the lab standard. They caught sleep almost every time, and they were poor at catching wake [1]. Put plainly, a device that simply assumed you were asleep all night would score well on the first metric. Sleep stage estimates were inconsistent, and the devices slipped further on the night the researchers deliberately disrupted sleep, which is the closest that study came to the nights you actually want measured.

On the other hand, a 2025 meta-analysis pooling 24 studies and 798 people found the nightly totals land closer than those epoch-by-epoch numbers suggest, and err the other way: wrist devices underestimated total sleep by about 17 minutes and overestimated time awake by about 13, and Fitbit's wake time didn't differ significantly from the lab [2]. Its conclusion is the practical one: These devices are useful for general patterns, not for precise measurement. Phone apps listening from the nightstand are weaker again. In a polysomnography study of four of them, none could identify REM sleep at all [3].

So read your numbers accordingly. Trends in total sleep and time in bed across weeks are genuinely useful. Last night's deep sleep percentage, or "you were awake for 47 minutes," is not precise enough to plan around.

There is also a cost to taking the score too seriously. Orthosomnia is the informal term clinicians gave it, in a small case series describing patients whose preoccupation with tracker data appeared to feed sleep anxiety, some of them spending longer in bed trying to improve the number [4]. A tracker earns its place next to a plan, where it can pre-fill a diary you confirm each morning, since the sleep you actually experienced is what the plan runs on. On its own, it hands you a nightly report card on one thing you cannot pass by trying harder.

Full guide: The Best Sleep Apps of 2026, Compared.

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Citations

1. Chinoy, E. D., Cuellar, J. A., Huwa, K. E., et al. (2021). Performance of seven consumer sleep-tracking devices compared with polysomnography. Sleep, 44(5), zsaa291. https://doi.org/10.1093/sleep/zsaa291 (Thirty-four healthy young adults across three laboratory nights, one of them under an experimental sleep-disruption protocol; epoch-by-epoch sensitivity ≥0.93, specificity 0.18–0.54, mixed sleep-stage agreement.)

2. Lee, Y. J., Lee, J. Y., Cho, J. H., Kang, Y. J., & Choi, J. H. (2025). Performance of consumer wrist-worn sleep tracking devices compared to polysomnography: A meta-analysis. Journal of Clinical Sleep Medicine, 21(3), 573–582. https://doi.org/10.5664/jcsm.11460 (Twenty-four studies, 798 participants. Versus polysomnography: total sleep time −16.9 minutes, sleep efficiency −4.7%, sleep latency +2.6 minutes, wake after sleep onset +13.3 minutes; no significant difference in wake after sleep onset for Fitbit. Authors conclude the devices remain useful for tracking general sleep patterns.)

3. Fino, E., Plazzi, G., Filardi, M., et al. (2020). (Not so) Smart sleep tracking through the phone: Findings from a polysomnography study testing the reliability of four sleep applications. Journal of Sleep Research, 29(1), e12935. https://doi.org/10.1111/jsr.12935

4. Baron, K. G., Abbott, S., Jao, N., Manalo, N., & Mullen, R. (2017). Orthosomnia: Are some patients taking the quantified self too far? Journal of Clinical Sleep Medicine, 13(2), 351–354. https://doi.org/10.5664/jcsm.6472