Wearables · Health metrics
Sleep efficiency and sleep stages
Sleep efficiency is the share of time in bed spent asleep. What it means, how wearables estimate sleep stages, and why stage data should be read with caution.
Written by LON6EVITY Editorial Team · Last updated
What sleep efficiency is
Sleep efficiency is total sleep time divided by time in bed. A lower value means more time lying awake.
Sleep stages
NHLBI describes sleep as cycling through non-REM stages (including deep sleep) and REM sleep several times a night, each with different roles.
How accurate are wearables?
Stages are formally scored from brain activity in a sleep lab. Consumer devices estimate them from movement, heart rate and sometimes temperature. The 2021 comparison by Chinoy et al. found that sleep stage accuracy varied considerably between devices.
Limitations
Wearable readings are estimates designed mainly for wellness and fitness. Accuracy varies by device, fit, skin, movement and model. They do not diagnose conditions; discuss concerning or persistent changes with a clinician.
Factors that can affect the result
- Time in bed
- Caffeine and alcohol
- Stress
- Environment
- Sleep disorders
Questions people commonly ask
- Should I worry about low deep sleep on my tracker?
- Stage estimates are the least accurate part of sleep tracking. Focus on duration, regularity and how you feel.
- When should I see a doctor about sleep?
- Loud snoring with pauses in breathing, persistent insomnia or excessive daytime sleepiness should be assessed.
Related topics
Bring your health data together
What does this mean for your own health data? Log your results, follow trends over time and bring an organised summary to your next doctor's appointment.
Sources
- How Sleep Works. National Heart, Lung, and Blood Institute (NIH).
- Performance of seven consumer sleep-tracking devices compared with polysomnography. Chinoy ED et al., Sleep, 2021.