A sleep cycle lasts about 90 minutes and runs through light, deep and REM sleep. Official sources disagree on the exact length: Germany’s IQWiG says 90 to 110 minutes, the US NHLBI 80 to 100. Most nights you go through four to six cycles, with more deep sleep early and more REM sleep later.
Dieser Artikel auf Deutsch: Schlafphasen: Ablauf, Zyklusdauer und Tabelle
Know the stages, and you can take your tracker’s sleep chart with a grain of salt and plan your mornings in cycles. To count back your bedtime in cycles, use the sleep calculator.
What are the stages of sleep?
Sleep comes in two kinds, REM and non-REM, and non-REM sleep has three stages. A cycle runs through non-REM into REM sleep, then starts over1,2. The stages differ in their brain waves1 and are scored in 30-second epochs3. Their names are N1, N2, N3 (deep or slow-wave sleep) and REM2,4. We give no minutes per stage, because REM stages get longer and deep-sleep stages shorter as the night goes on5, so a single minute value would mislead.
What “stage 4” used to mean
Some current pages number the stages in a row and count REM after N1, N2 and N3; in the sources we cite, the three stages belong to non-REM sleep1,2. “Stage 4” comes from the 1968 manual of Rechtschaffen and Kales, which split deep sleep into S3 and S4; the American Academy of Sleep Medicine (AASM) rules group both into N3, so in an older study, stage 4 is deep sleep3,4,6.
How long is a sleep cycle?
About 90 minutes is the usual rule of thumb7. Official figures differ. Germany’s Institute for Quality and Efficiency in Health Care (IQWiG) says 90 to 110 minutes, or around five cycles in eight hours5. The US National Heart, Lung, and Blood Institute (NHLBI) says 80 to 100 minutes, usually four to six times a night2.
Measured in 205 healthy adults aged 18 to 75, a classical cycle lasted 90.1 minutes on average, with a standard deviation of 24.9 minutes7. The spread covers all cycles recorded, so single cycles were often clearly shorter or longer (our reading)7.
The sleep calculator assumes cycles of 90 minutes plus a fixed 15 minutes to fall asleep, and it calls both rules of thumb. It offers six, five or four cycles2,5,7.
The sleep stages at a glance
In one pooled study, healthy adults spent the largest share of the night in N2, the rest in deep sleep, REM, N1 and wake7.
Means for 205 healthy adults aged 18 to 75, pooled from five polysomnography datasets (four in a sleep lab, one at home). Depending on the dataset, people with over 25% wake time after falling asleep or no REM sleep were excluded.| Stage | What happens | Share of the night (measured) | When in the night? |
|---|
| N1 (light sleep) | Very light sleep, easily woken5 | 7.9%7 | At the transition from waking to sleep2 |
| N2 (light sleep) | Brain activity slows, with short bursts5 | 45.1%7 | About half of each cycle5, more than any other stage1 |
| N3 (deep sleep, slow-wave sleep) | Named after a brain-wave pattern2; noise disturbs it less easily5; per NINDS, the deep sleep “you need to feel refreshed in the morning”1 | 20.9% (slow-wave sleep)7 | Longer periods in the first half of the night1,2 |
| REM sleep | Eyes twitch, brain activity close to waking, muscles normally limp2; sleep lighter again5; most dreaming, some also in non-REM1 | 18.6%7 | More and longer later in the night1,2; first about 90 minutes after falling asleep1 |
| Wake after falling asleep | Some wake after a cycle, others sleep through5 | 7.0%7 | Possible briefly, between cycles2 |
Per NINDS, memory consolidation most likely requires both non-REM and REM sleep1. Levels also differ by study: one scored by the 2007 AASM criteria found higher N1 and N3 and lower N2 and REM shares than previous studies4, one reason tables online disagree (our reading).
How the stages shift across the night
Deep sleep comes early, REM sleep late1,2. In the table’s pooled study, cycle length followed an inverted U across the night: mid-night cycles ran longest7. There, 47 of the 205 healthy adults (23%) had a first cycle without REM sleep, most often in the youngest dataset: 19 of its 34 young adults aged 18 to 35, recorded at home7.
REM isn’t the only stage with dreams: dreaming also occurs in non-REM sleep, and studies found dream reports after up to 70% of awakenings from it8.
How much deep sleep should you get?
None of the sources we checked gives a target. Deep-sleep shares vary widely between healthy people4, and whether they fall with age is disputed: large meta-analyses disagree9,10, and the later one found no significant change with age in N2, N3 or REM shares9. A low number on your tracker is not a diagnosis.
Our rough estimate for the table’s 205 healthy adults (average age 36.7, five datasets) is about 100 minutes of slow-wave sleep a night: its share of the four sleep stages times the 438 minutes of average total sleep time7. Calculated from the sample’s averages, it is not a measured average or a target, and the youngest dataset, recorded at home, pulls it up with markedly more slow-wave sleep than the other four7.
An earlier large meta-analysis pooled 65 studies published between 1960 and 2003 that recorded sleep by polysomnography or actigraphy (a movement-based research measure), with 3,577 participants aged 5 to 102: in adults, slow-wave and REM shares decreased with age, and after age 60, of every measure it pooled, total sleep time included, only sleep efficiency kept falling significantly. How carefully participants were screened strongly changed the effect sizes10. The later one, 169 studies published between 2007 and 2016 with 5,273 healthy adult participants, scored in the lab by the AASM criteria of 2007 or 2012, is the one that found no significant age change in the N2, N3 and REM shares9. In 100 healthy sleepers aged 19 to 77, recorded for one night in a hospital sleep lab and scored by the 2007 AASM criteria, the group over 60 (24 people) had lower medians than the youngest group (20 people): deep sleep 14.9% (range 2.4 to 35.6) against 20.7% (range 15.2 to 37.5), REM sleep 10.3% against 15.5%4. The NHLBI says slow-wave sleep continues to decrease through adulthood and older people may not have any at all2. That page speaks of amount; the earlier meta-analysis’s stage result is about shares10.
Can a sleep tracker measure your sleep stages?
In one sleep-lab comparison with polysomnography, the devices tested were good at detecting sleep and inconsistent on sleep stages11. There, 34 healthy young adults (22 women, average age 28.1) slept three nights in the lab, one of them disrupted, while four wearable and three nonwearable devices were tested11. Wake detection was only low to medium, and the devices tended to do worse on poorer or disrupted nights11. Most matched or beat actigraphy on sleep and wake measures, while some did worse11. Several split non-REM into just “light” and “deep,” lumping N1 and N2 together11.
Our advice: use a tracker for when and how long you slept, and read its stage minutes as an estimate.
When to wake up: sleep cycles and your alarm
Some people wake fully or partly after a cycle, others sleep until morning5, and you may wake briefly between cycles2.
A review of sleep inertia, the grogginess after waking, reports studies linking deeper sleep at waking with more grogginess, mostly after longer naps and under high sleep pressure6. Others found no such link, also under controlled sleep-wake conditions, after long periods awake and particularly often in nap studies6. The authors find it difficult to draw a clear conclusion and write that more recent literature suggests the link may not be as robust as first thought6.
We think the 90 minutes are a useful rule of thumb for planning a wake-up window and a poor fit for timing an alarm to the minute, because the official ranges differ, cycles spread widely around the measured average, and average cycle length changes across the night2,5,7.
An example with the sleep calculator: you’re back at work after parental leave and must be up at 6 a.m. on weekdays. In “Wake up” mode, it counts back your cycles of 90 minutes plus 15 minutes to fall asleep: 8:45 p.m. for six cycles, 11:45 p.m. for four, and for five2,5:
10:15 p.m.
Frequently asked questions
How many sleep cycles do I need per night?
The sources describe what is typical: four to six a night2,7 or around five in eight hours5. A US National Sleep Foundation expert panel considers 7 to 9 hours appropriate for young adults and adults, as guidance for healthy people without a sleep disorder12: just under five to six 90-minute cycles (4.7 to 6, our calculation).
Is REM sleep the deepest?
No. Deep sleep is N3, or slow-wave sleep2. In REM sleep, brain activity resembles waking and your muscles normally go limp so you don’t act out your dreams2, and sleep becomes lighter again5.
How many hours of REM sleep do you need?
None of the sources we checked gives a target. In one pooled study of 205 healthy adults aged 18 to 75 (five datasets), REM sleep took 18.6% of the night on average7.
Do older adults need less sleep?
Usually not. NINDS says most adults need 7 to 9 hours a night, even older people1. The National Sleep Foundation panel’s range for older adults ends an hour lower, at 7 to 8 hours: a recommendation for healthy people, not a measurement12.
Is the length of everyone’s sleep cycles the same?
No. In one pooled study, cycle length varied a lot (90 minutes on average, standard deviation 25) and changed across the night on average7. By age, 21 children and adolescents aged 8 to 17 had shorter cycles than 24 young adults aged 23 to 257, and in the first weeks of life a cycle lasts 50 to 60 minutes13.
Your wake-up window
Our advice: if you plan in cycles, plan a wake-up window instead of an exact minute, and count back with the sleep calculator.
Sources
- National Institute of Neurological Disorders and Stroke (NIH): Brain Basics: Understanding Sleep. Last reviewed February 25, 2025. ninds.nih.gov/health-information/public-education/brain-basics/brain-basics-understanding-sleep (retrieved November 8, 2026)
- National Heart, Lung, and Blood Institute (NIH): How Sleep Works, Sleep Phases and Stages. Last updated March 24, 2022. nhlbi.nih.gov/health/sleep/stages-of-sleep (retrieved November 8, 2026)
- Silber MH, Ancoli-Israel S, Bonnet MH, et al. The visual scoring of sleep in adults. J Clin Sleep Med 2007;3(2):121-131. (abstract) doi:10.5664/jcsm.26814 (retrieved November 8, 2026)
- Mitterling T, Högl B, Schönwald SV, et al. Sleep and Respiration in 100 Healthy Caucasian Sleepers: A Polysomnographic Study According to American Academy of Sleep Medicine Standards. Sleep 2015;38(6):867-875. pmc.ncbi.nlm.nih.gov/articles/PMC4434553 (retrieved November 8, 2026)
- IQWiG (Institute for Quality and Efficiency in Health Care): What is “normal” sleep? InformedHealth.org, updated August 1, 2024. informedhealth.org/what-is-normal-sleep.html (retrieved November 8, 2026)
- Hilditch CJ, McHill AW. Sleep inertia: current insights. Nat Sci Sleep 2019;11:155-165. pmc.ncbi.nlm.nih.gov/articles/PMC6710480 (retrieved November 8, 2026)
- Rosenblum Y, Jafarzadeh Esfahani M, Adelhöfer N, et al. Fractal cycles of sleep, a new aperiodic activity-based definition of sleep cycles. eLife 2025;13:RP96784. pmc.ncbi.nlm.nih.gov/articles/PMC11717360 (retrieved November 8, 2026)
- Siclari F, Baird B, Perogamvros L, et al. The neural correlates of dreaming. Nat Neurosci 2017;20(6):872-878. pmc.ncbi.nlm.nih.gov/articles/PMC5462120 (retrieved November 8, 2026)
- Boulos MI, Jairam T, Kendzerska T, et al. Normal polysomnography parameters in healthy adults: a systematic review and meta-analysis. Lancet Respir Med 2019;7(6):533-543. (abstract) doi:10.1016/S2213-2600(19)30057-8 (retrieved November 8, 2026)
- Ohayon MM, Carskadon MA, Guilleminault C, Vitiello MV. Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals: developing normative sleep values across the human lifespan. Sleep 2004;27(7):1255-1273. (abstract) doi:10.1093/sleep/27.7.1255 (retrieved November 8, 2026)
- Chinoy ED, Cuellar JA, Huwa KE, et al. Performance of seven consumer sleep-tracking devices compared with polysomnography. Sleep 2021;44(5):zsaa291. pmc.ncbi.nlm.nih.gov/articles/PMC8120339 (retrieved November 8, 2026)
- Hirshkowitz M, Whiton K, Albert SM, et al. National Sleep Foundation's sleep time duration recommendations: methodology and results summary. Sleep Health 2015;1(1):40-43. (abstract) doi:10.1016/j.sleh.2014.12.010 (retrieved October 10, 2026)
- El Shakankiry HM. Sleep physiology and sleep disorders in childhood. Nat Sci Sleep 2011;3:101-114. pmc.ncbi.nlm.nih.gov/articles/PMC3630965 (retrieved November 8, 2026)
Published November 9, 2026
This article is not medical advice. If sleep problems persist, talk to a doctor.
Keep exploring
Find the bedtime that fits your alarm in the sleep calculator. To see how much of an afternoon coffee is still working at bedtime, read our guide to how long caffeine lasts. If thoughts keep you awake, read how to stop overthinking, and to wind down, try the breathing exercise timer.
