The percentage of time in bed actually spent asleep. A core clinical sleep metric and one of the most actionable numbers your wearable reports.
This page will help you read your own sleep efficiency percentage correctly — what a single night's number can and can't tell you, and how it compares to the trend your device builds over weeks.
Sleep efficiency is calculated as: (Total sleep time ÷ Time in bed) × 100. A person who spends 8 hours in bed but sleeps for only 6.4 hours has a sleep efficiency of 80%.
The metric originated in polysomnography (PSG) research as a way to distinguish time in bed from actual restorative sleep. It remains one of the core metrics in clinical sleep assessment and cognitive behavioral therapy for insomnia (CBT-I).
| Efficiency % | Clinical Category | Interpretation |
|---|---|---|
| ≥ 90% | Excellent | Highly consolidated sleep |
| 85–89% | Normal | Clinically typical for healthy adults |
| 75–84% | Below average | May indicate sleep fragmentation |
| < 75% | Poor | Clinical threshold for insomnia diagnosis |
Source: Morin CM et al. Psychological and pharmacological treatments for insomnia. Am J Psychiatry. 2006. American Academy of Sleep Medicine guidelines.
| Age Group | Mean Sleep Efficiency | Typical Range |
|---|---|---|
| 18–30 | 89% | 82–95% |
| 31–45 | 87% | 79–93% |
| 46–60 | 84% | 74–91% |
| 61–75 | 80% | 68–88% |
| 75+ | 75% | 62–84% |
Source: Ohayon MM et al. Meta-analysis of quantitative sleep parameters across the lifespan. Sleep. 2004.
| Myth | Reality |
|---|---|
| "100% sleep efficiency is the goal" | Values above ~98% are unusual even in healthy sleepers; some brief wake is normal and not a flaw to eliminate. |
| "A low score one night means bad sleep health" | Single-night dips are common and often explained by travel, alcohol, or stress — the multi-week trend is the meaningful signal. |
| "Every device measures it the same way" | Underlying wake detection differs by sensor and algorithm, so efficiency percentages are not directly comparable across brands. |
| "Higher efficiency always means better sleep" | Efficiency says nothing about sleep stage composition — someone can hit 92% efficiency with very little deep or REM sleep. |