Most of us judge a night’s sleep by how we feel the next morning. Some nights you wake up clear-headed and ready to go. Others you wake up foggy and slow, even though you slept just as long.
The hours themselves are only part of it. Through the night, sleep moves through distinct stages, and 2 of them, deep sleep and rapid eye movement (REM) sleep, are thought to carry out much of the brain's and body's overnight recovery. If you wear a sleep tracker, you may already see figures for both each morning.
So how much deep sleep and REM do you actually need, and does that change as you get older?
What Happens Across a Night of Sleep?
Sleep runs in cycles of roughly 90 minutes, usually 4 to 6 a night (1). In each cycle you move from light sleep into deep sleep, back through light sleep and then into REM. Sleep is sometimes split into 4 or 5 stages, but most trackers use these 3.
What Is Light Sleep?
Light sleep makes up more than half of your sleep. Your heart rate and body temperature drop, and short bursts of brain activity are thought to help store memories and skills (1).
What Is Deep Sleep?
Deep sleep, also called slow-wave sleep, is the hardest stage to wake from, and if you are woken during it you may feel groggy for up to 1 hour. It is thought to help the body repair tissue, build bone and muscle and support the immune system (1), and has been linked to storing new memories (2).
What Is REM Sleep?
REM is named after the rapid eye movements that happen during it. Your brain becomes almost as active as when you are awake, most of your muscles are temporarily paralysed and most vivid dreaming happens (1). REM appears to help the brain process emotional experiences (3).
When Does Each Stage Happen?
Most deep sleep happens in the first third of the night, while REM periods get longer towards morning (4). The first REM period starts about 90 minutes after you fall asleep and lasts only a few minutes, while the last can run for up to 1 hour (1, 4). So cutting your night short costs you more REM than deep sleep.
An illustrative 7.5-hour night for a healthy adult. The shaded area is the first third of the night. Brief awakenings are normal and become more frequent with age.
We cover what each stage does for recovery in Deep Sleep or REM: Which Matters More for Recovery?
How Much Deep Sleep and REM Do You Need?
There is no official target for minutes of deep or REM sleep. Medical guidance focuses on total sleep instead: 7 hours or more a night, on a regular basis, for adults aged 18 to 60 (5). Stanford neuroscientist Dr Andrew Huberman and UC Berkeley sleep scientist Dr Matthew Walker don't set stage targets either. In his 2024 series on Huberman's podcast, Walker recommends 7 to 9 hours a night with the emphasis on sleeping without frequent waking (6), while Huberman's own Sleep Toolkit centres on waking at the same time every day and getting outdoor light soon after (7).
Sleep studies do give a useful guide to what is normal, though. A 2019 review of 169 sleep lab studies, covering more than 5,000 healthy adults, found that deep sleep and REM each make up about 20% of total sleep, with light sleep making up most of the rest (8). On average, that meant:
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Adults aged 18 to 34: about 6 hours 50 minutes of sleep, including about 90 minutes of deep sleep and 80 minutes of REM.
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Adults aged 65 to 79: just under 6 hours of sleep, including about 70 minutes of deep sleep and 60 minutes of REM.
Older adults got fewer minutes of each stage mainly because they slept less overall. The share of the night spent in each stage barely changed.
How Do You Work Out Your Own Range?
As a rough guide, expect about a fifth of the time you are actually asleep (not your time in bed) to be deep sleep, and about a fifth to be REM. That gives:
- 6 hours of sleep: about 70 minutes each of deep sleep and REM.
- 7 hours of sleep: about 85 minutes each.
- 8 hours of sleep: about 95 minutes each.
These are averages, and the 25% often quoted online (1) is a little higher than the review found, so being slightly below it is normal.
Why Can the Same Hours Feel So Different?
How often you wake in the night seems to matter more than how much deep sleep you get. In a study of 206 healthy adults aged 20 to 84, people rated their sleep as worse the more often they woke up, and better when they had more REM. Their amount of deep sleep made no clear difference to how well they felt they had slept (9). Being woken during deep sleep can also leave you groggy for a while, as we saw above. This fits Walker's focus on sleeping without frequent waking.
How Does Sleep Change With Age?
As we get older, our body clock tends to shift earlier. Adults aged 65 and over typically fall asleep about 1 hour earlier and wake about 1.5 hours earlier than adults in their 20s, and their sleep is more easily broken. Women tend to hold on to their deep sleep better than men, while men wake more often in the night (1).
But what happens when someone's deep sleep keeps dropping over the years?
Why Do Longevity Researchers Care About Sleep Stages?
In 346 adults over 60 from the Framingham Heart Study, each 1 percentage point drop in deep sleep per year was linked to a 27% higher risk of dementia (10). In 2,675 older men followed for about 12 years, each 5% reduction in REM was linked to a 13% higher risk of death from any cause (11).
Both studies are observational, so neither proves that losing these stages causes the problems. Early changes in the brain may reduce deep sleep rather than the other way round, and low REM may be a marker of poor health more than a direct cause.
Can You Trust Your Sleep Tracker's Numbers?
Only roughly. Trackers are good at telling when you are asleep, but when 6 wearable devices, including the Apple Watch and Oura Ring, were tested against a sleep lab, they matched its stage readings only 50 to 65% of the time (12). Treat a single night's figures as an estimate. Rather than chasing a higher number, aim for enough regular sleep for your brain to complete its normal cycles, as there is no well-established way to boost a single stage on its own. Our next article, What Affects Sleep Quality, and How Can You Improve It?, looks at what helps.
The Takeaway
Deep sleep and REM have wide normal ranges rather than targets, and you tend to get fewer minutes of both as you get older. If you regularly sleep 7 hours or more, keep a steady wake time and wake up rested, a low tracker figure is not a reason to worry. Do speak to a doctor if poor sleep comes with persistent daytime sleepiness, loud snoring, pauses in breathing that someone else notices, ongoing insomnia, or another lasting change in how you feel.
This article is not medical advice.
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Literature Sources
- Patel AK, Reddy V, Shumway KR, Araujo JF. Physiology, Sleep Stages. StatPearls. Treasure Island (FL): StatPearls Publishing; 2024. https://www.ncbi.nlm.nih.gov/books/NBK526132/
- Diekelmann S, Born J. The memory function of sleep. Nature Reviews Neuroscience. 2010;11(2):114-126. https://doi.org/10.1038/nrn2762
- Walker MP, van der Helm E. Overnight therapy? The role of sleep in emotional brain processing. Psychological Bulletin. 2009;135(5):731-748. https://doi.org/10.1037/a0016570
- Institute of Medicine (US) Committee on Sleep Medicine and Research; Colten HR, Altevogt BM, editors. Sleep Physiology. In: Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem. Washington (DC): National Academies Press; 2006. https://www.ncbi.nlm.nih.gov/books/NBK19956/
- Watson NF, Badr MS, Belenky G, Bliwise DL, Buxton OM, Buysse D, et al. Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society. Sleep. 2015;38(6):843-844. https://doi.org/10.5665/sleep.4716
- Huberman A, Walker M. Guest Series | Dr. Matt Walker: The Biology of Sleep & Your Unique Sleep Needs. Huberman Lab podcast. 3 April 2024.
- Huberman A. Sleep Toolkit: Tools for Optimizing Sleep & Sleep-Wake Timing. Huberman Lab podcast, episode 84. 2022. https://www.hubermanlab.com/episode/sleep-toolkit-tools-for-optimizing-sleep-and-sleep-wake-timing
- Boulos MI, Jairam T, Kendzerska T, Im J, Mekhael A, Murray BJ. Normal polysomnography parameters in healthy adults: a systematic review and meta-analysis. The Lancet Respiratory Medicine. 2019;7(6):533-543. https://doi.org/10.1016/S2213-2600(19)30057-8
- della Monica C, Johnsen S, Atzori G, Groeger JA, Dijk DJ. Rapid Eye Movement Sleep, Sleep Continuity and Slow Wave Sleep as Predictors of Cognition, Mood, and Subjective Sleep Quality in Healthy Men and Women, Aged 20-84 Years. Frontiers in Psychiatry. 2018;9:255. https://doi.org/10.3389/fpsyt.2018.00255
- Himali JJ, Baril AA, Cavuoto MG, Yiallourou S, Wiedner CD, Himali D, et al. Association Between Slow-Wave Sleep Loss and Incident Dementia. JAMA Neurology. 2023;80(12):1326-1333. https://doi.org/10.1001/jamaneurol.2023.3889
- Leary EB, Watson KT, Ancoli-Israel S, Redline S, Yaffe K, Ravelo LA, et al. Association of Rapid Eye Movement Sleep With Mortality in Middle-aged and Older Adults. JAMA Neurology. 2020;77(10):1241-1251. https://doi.org/10.1001/jamaneurol.2020.2108
- Miller DJ, Sargent C, Roach GD. A Validation of Six Wearable Devices for Estimating Sleep, Heart Rate and Heart Rate Variability in Healthy Adults. Sensors. 2022;22(16):6317. https://doi.org/10.3390/s22166317
