Sleep metrics to pay attention to.

Experts say three sleep metrics — time in sleep stages, nighttime awakenings, and time asleep versus time in bed — are most useful for interpreting tracker reports and linking behavior to sleep quality.

Sleep trackers now give users detailed nightly reports, but the numbers can be confusing. Experts say three metrics are particularly useful for interpreting that data. Tim Rosa of Somnee and Dr. Michael Gradisar of Sleep Cycle explain what those measures reflect. Smartwatches and rings are becoming more common and closer to lab-grade tracking, with one in four people owning a smartwatch in 2025, according to SQ Magazine. Highlights: - Time in sleep stages: REM and deep sleep are central measures; the article cites ideal nightly ranges of about 1.5–2.5 hours for REM and 1–2 hours for deep sleep. - REM is linked to memory, alertness and mental sharpness, while deep sleep is tied to physical recovery and performance readiness, according to Tim Rosa. - Nighttime awakenings can fragment sleep cycles and are useful to monitor because patterns may point to triggers such as late-night snacks, caffeine, stress or screen time. - Alcohol is reported by Dr. Michael Gradisar to reduce REM sleep within hours of consumption. - Sleep duration versus actual sleep: modern trackers distinguish time in bed from time asleep and use actual sleep time to calculate sleep scores, which can reveal bedtime activities like prolonged scrolling. Summary: Paying attention to these three metrics can help people connect habits and events to sleep outcomes and observe short-term changes after behavior changes are reported. Undetermined at this time.