Apple Watch sleep score shows about 90 minutes of deep sleep a night, and doctors say that can be normal

Two sleep experts told the author that one to two hours of deep sleep is typical for most adults, and the Apple Watch uses motion and an algorithm to estimate sleep stages but is not exact.

I checked my Apple Watch and noticed deep sleep often totals about 90 minutes a night even when I sleep eight hours or more. The watch reports four stages: Awake, Core (light) Sleep, REM, and Deep Sleep. Two sleep experts, Dr. Jade Wu and Dr. Chris Allen, explained what deep sleep is and how much is typical. Their guidance framed the 90-minute figure as within normal expectations for many adults. Key points: - The Apple Watch separates sleep into Awake, Core (light), REM, and Deep Sleep stages. - Deep sleep (slow-wave sleep) is the most physically restorative non-REM stage and is linked to growth hormone release, tissue repair, and memory consolidation. - For most healthy adults, deep sleep commonly makes up about 15–25% of total sleep time, roughly one to two hours per night. - Deep sleep amounts usually decline with age, though the biological need for restorative sleep remains. - The Apple Watch uses motion and breathing-related signals fed to an algorithm trained on polysomnography data to estimate stages, and experts say those estimates are approximations; they also reported certain signs (for example loud snoring, daytime sleepiness, morning headaches) can be associated with sleep disorders. Summary: The experts told the author that roughly 90 minutes of deep sleep aligns with typical adult sleep architecture, and the Apple Watch provides useful but imprecise estimates of sleep stages. Undetermined at this time.