Deep Sleep Stage

% of sleep time

Percentage of sleep time in slow-wave sleep (N3), the most physically restorative stage. Critical for tissue repair, immune function and hormonal regulation.

Typical optimal range 13% - 23%

Population median 16%

Judge deep sleep against your own age-adjusted baseline, not a fixed target.

Key factors

Physical exertion earlier in the day
Sleep timing relative to circadian rhythm
Body temperature at sleep onset

What affects this metric

Aerobic exercise and heat exposure earlier in the day increase it.
Sleep debt causes a deep sleep rebound on the following nights.
Untreated sleep apnea fragments deep sleep.
A late bedtime cuts deep sleep, since it concentrates early in the night.
Alcohol reduces deep sleep quality even when duration looks normal.

References

Peer-reviewed sources supporting the key factors, contributing factors, and typical optimal range shown above.

Ohayon MM, Carskadon MA, Guilleminault C, Vitiello MV. Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals. Sleep. 2004;27(7):1255–1273. doi.org/10.1093/sleep/27.7.1255
Kredlow MA, Capozzoli MC, Hearon BA, Calkins AW, Otto MW. The effects of physical activity on sleep: a meta-analytic review. Journal of Behavioral Medicine. 2015;38(3):427–449. doi.org/10.1007/s10865-015-9617-6
Haghayegh S, Khoshnevis S, Smolensky MH, Diller KR, Castriotta RJ. Before-bedtime passive body heating by warm shower or bath to improve sleep: a systematic review and meta-analysis. Sleep Medicine Reviews. 2019;46:124–135. doi.org/10.1016/j.smrv.2019.04.008
Ebrahim IO, Shapiro CM, Williams AJ, Fenwick PB. Alcohol and sleep I: effects on normal sleep. Alcoholism: Clinical and Experimental Research. 2013;37(4):539–549. doi.org/10.1111/acer.12006

This guide is general information, not medical advice. Talk to your clinician about your own results.