How Much Deep and REM Sleep Do You Need?

There’s no target amount of deep or REM sleep that guidelines recommend. In sleep laboratories, healthy adults typically spend roughly a fifth of the night in REM sleep and a smaller share, often around 15% to 20%, in deep sleep, with wide differences between people. The amounts mostly look after themselves when you sleep enough and regularly, and watches estimate them too roughly for one night’s numbers to mean much.

This article is general information, not medical advice.

What Each Stage Does

Sleep cycles through stages about every 90 minutes:

• Light sleep (N1 and N2) makes up about half of the night or more.
• Deep sleep (N3, slow-wave sleep) comes mostly in the first half of the night. It’s when the brain’s electrical waves are slowest and the body is hardest to wake, and it’s linked to physical recovery and the release of growth hormone.
• REM sleep comes in longer periods towards the morning. Most vivid dreaming happens then, and it’s linked to memory and emotional processing.

Because deep sleep comes early and REM late, a short night cuts REM most, and going to bed late after a fixed alarm costs REM too.

Does It Change With Age?

The evidence isn’t fully settled:

• In a 2004 meta-analysis of sleep studies from childhood to old age, Ohayon and colleagues found that the share of deep sleep and REM sleep fell with age in adults, while light sleep and time awake rose, with most of the change before 60.
• In a 2019 meta-analysis of 169 sleep studies in 5,273 healthy adults, Boulos and colleagues found that total sleep time and efficiency fell, and time awake rose, with each decade of age, but the shares of deep and REM sleep didn’t change significantly.

Both found sleep becomes lighter and more broken with age; whether deep sleep itself declines depends partly on how carefully the people studied were screened for health problems.

What Moves the Stages

• Sleep debt raises deep sleep on the next night, as the body catches up.
• Alcohol delays the first REM period and, at moderate and high doses, reduces REM over the night, according to Ebrahim and colleagues’ review; see How Does Alcohol Affect Your Sleep?
• Some medicines, including many antidepressants, suppress REM.
• Sleep apnea fragments sleep and can reduce deep and REM sleep.

Why Not to Chase the Numbers

Consumer devices estimate stages from movement and heart rate, not brain waves, and they’re least accurate at telling deep and REM sleep apart from light sleep; see How Accurate Are the Sleep Stages From Your Watch or Ring? Baron and colleagues described patients whose efforts to perfect their tracker’s sleep data made their sleep worse, and named it orthosomnia. Total sleep, regular times, and how you feel are better guides.

Following It in Kaizora

Kaizora keeps Light Sleep Time, Deep Sleep Time, and REM Sleep Time from your watch or ring as spans across each night, on the Sleep page, where they’re charted stacked by night. The Kaizora Sleep Score compares your deep and REM share with your own 60-day baseline, not with a population target, for exactly this reason: what’s normal varies from person to person and device to device.

The Short Version

• No guideline sets a target for deep or REM sleep.
• REM is roughly a fifth of a night; deep sleep is a smaller share, mostly early in the night.
• Short nights cut REM most; alcohol delays and reduces it.
• Watch estimates are rough; follow your own trend, not one night.

Sources

• Ohayon MM et al., “Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals: developing normative sleep values across the human lifespan,” Sleep 27, no. 7 (2004): 1255–1273. doi:10.1093/sleep/27.7.1255
• Boulos MI et al., “Normal polysomnography parameters in healthy adults: a systematic review and meta-analysis,” The Lancet Respiratory Medicine 7, no. 6 (2019): 533–543. doi:10.1016/S2213-2600(19)30057-8
• Baron KG et al., “Orthosomnia: are some patients taking the quantified self too far?” Journal of Clinical Sleep Medicine 13, no. 2 (2017): 351–354. doi:10.5664/jcsm.6472
• Ebrahim IO et al., “Alcohol and sleep I: effects on normal sleep,” Alcoholism: Clinical and Experimental Research 37, no. 4 (2013). doi:10.1111/acer.12006