Stages of Sleep: N1, N2, Deep Sleep and REM Explained

There are four stages of sleep: three stages of non-REM sleep (N1, N2 and N3, also called deep sleep) and REM sleep. Your brain moves through all four in cycles of roughly 90 to 110 minutes, four to five times a night, with deep sleep concentrated early in the night and REM sleep getting longer toward morning. Light N2 sleep makes up about 45% of the night, deep N3 sleep and REM sleep about 25% each, and N1 about 5% (Patel and colleagues, 2024). This guide explains what happens in each stage, how a sleep cycle works, what sleep trackers mean by core sleep, and how your stages change with age.

It is educational, not medical advice.

Key Takeaways

Four stages, two types: non-REM sleep has three stages (N1 to N3), and REM sleep is the fourth (Patel and colleagues, 2024).
Cycles repeat: a typical night has four to five cycles of about 90 to 110 minutes each (Patel and colleagues, 2024).
Deep sleep comes first, REM comes later: as the night goes on, deep sleep shortens and REM periods lengthen, from about 10 minutes to up to an hour (Patel and colleagues, 2024).
Stages shift with age: in adults, deep sleep and REM sleep make up a smaller share of the night with age, while light sleep increases (Ohayon and colleagues, 2004).

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What Are the Stages of Sleep?

Sleep has two main types: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. NREM sleep is divided into three stages, N1 to N3, each with its own brain wave pattern, muscle tone and eye movements (Patel and colleagues, 2024). Older sources describe four NREM stages; stages 3 and 4 are now combined into N3, which is why you may see the stages of sleep listed as four or five.

Stage	Share of the night	Brain waves	What happens
N1 (light sleep onset)	About 5%	Theta waves	Drifting off; lasts about 1 to 5 minutes
N2 (light sleep)	About 45%	Sleep spindles and K-complexes	The largest share of the night; first period about 25 minutes
N3 (deep sleep)	About 25%	Delta waves, slowest and largest	Hardest stage to wake from
REM sleep	About 25%	Fast, wake-like activity	Muscles go slack; most vivid dreams

Source for the table: (Patel and colleagues, 2024). Shares are typical values for young adults and change with age (Ohayon and colleagues, 2004).

Stage 1 (N1): Drifting Off

N1 is the shift from wakefulness into sleep. While you are awake with your eyes open, fast beta waves dominate; as you get drowsy and close your eyes, slower alpha waves take over, and in N1 these give way to low-voltage theta waves. N1 lasts about 1 to 5 minutes and makes up around 5% of total sleep (Patel and colleagues, 2024). It is easy to be woken from N1, and many people do not realize they were asleep. Our guide to falling asleep fast covers what helps you get here.

Stage 2 (N2): Light Sleep

N2 is where you spend the most time, about 45% of the night. Its brain waves include sleep spindles, brief powerful bursts of activity, and K-complexes, long slow waves that last about a second. The first N2 period lasts around 25 minutes and later ones get longer (Patel and colleagues, 2024). Sleep trackers often call N1 and N2 light sleep or core sleep.

Stage 3 (N3): Deep Sleep

N3 is the deepest stage of non-REM sleep, also called slow-wave sleep. Its delta waves are the slowest and largest of the night, and it is the hardest stage to wake from (Patel and colleagues, 2024). Deep sleep is concentrated in the first cycles and shrinks as the night goes on. For how much deep sleep you need and how to protect it, see our guide to how much deep sleep you need.

REM Sleep

The first REM period usually starts about 90 minutes after you fall asleep and lasts around 10 minutes; each later REM period is longer, with the last lasting up to an hour. During REM, brain activity looks close to waking, the eyes move quickly, and the skeletal muscles go slack, which keeps you from acting out dreams (Patel and colleagues, 2024). REM is the stage most linked with vivid dreaming, but dreams also happen in non-REM sleep: brain recordings have caught dream reports from both (Siclari and colleagues, 2017).

Diagram: an example night of about five sleep cycles moving through N1, N2, deep sleep (N3) and REM; deep sleep is longest early in the night and REM periods grow longer toward morning.

When short nights keep cutting into the later cycles, the missed sleep adds up; our guide to sleep debt explains how to recover.

How a Sleep Cycle Works

A typical night has four to five sleep cycles, each lasting roughly 90 to 110 minutes (Patel and colleagues, 2024). A cycle usually moves from N1 to N2 to N3, back up through N2, and into REM. Early cycles hold most of the deep sleep; later cycles hold longer REM periods and less deep sleep (Patel and colleagues, 2024). That means a short night cuts mostly into the REM-rich cycles near morning, and waking during deep sleep, as can happen with a long nap, tends to leave you groggy; see our guide to how long a nap should be.

Is REM Sleep Deep Sleep?

No. Deep sleep is N3, the slow-wave stage of non-REM sleep, when the brain is quietest and you are hardest to wake. REM sleep is a separate stage with wake-like brain activity, rapid eye movements and relaxed muscles (Patel and colleagues, 2024). Both matter, and they peak at different times of the night.

Core, Light, Deep and REM: Reading Your Sleep Tracker

Most trackers group N1 and N2 as light or core sleep, and report deep sleep and REM sleep separately. In a laboratory test of seven consumer sleep trackers against polysomnography, the devices detected sleep well, but their sleep stage estimates were inconsistent, and they did worse on nights of disrupted sleep (Chinoy and colleagues, 2021). Use your tracker's stage numbers to spot trends over weeks, not to judge a single night.

For the total hours each age group needs, see our guide how much sleep do I need.

How Sleep Stages Change With Age

A meta-analysis of 65 studies covering 3,577 people aged 5 to 102 found that in adults, total sleep time, sleep efficiency, the share of slow-wave (deep) sleep and the share of REM sleep all fall with age, while the share of light N1 and N2 sleep and time awake after falling asleep rise (Ohayon and colleagues, 2004). Some decline in deep sleep is a normal part of getting older.

What Affects Your Sleep Stages

Alcohol: alcohol shortens the time to fall asleep and deepens the first half of the night, but it delays the first REM period, lowers total REM sleep at moderate and high doses, and disrupts the second half of the night (Ebrahim and colleagues, 2013).
Short or irregular sleep: because REM sleep is concentrated in the later cycles, cutting your night short trims REM most (Patel and colleagues, 2024). A regular schedule helps; see our guide to fixing your sleep schedule.
Waking in the night: if you often wake in the early hours, our guide to waking up at 3am explains common causes.
Age: lighter, more broken sleep is more common as you get older (Ohayon and colleagues, 2004).

For 11 research-backed habits that improve sleep across all its stages, see our guide on how to sleep better.

Where Our Products Fit

No supplement lets you choose your sleep stages, and the habits above matter most. Melatonin is the hormone your body uses to signal night; our Melatonin Nasal Spray provides 200 mcg of melatonin with 17 mg of L-theanine per two-spray serving, used 15 to 30 minutes before bed. The Sleep Stack combines Melatonin Nasal Spray, Theanine Nasal Spray and Lithium Orotate in one evening routine. Learn more on our melatonin ingredient page and our sleep health hub. Talk to your doctor before starting a supplement if you are pregnant, breastfeeding or take medication.

When to See a Doctor

See a doctor if you snore loudly or stop breathing or gasp during sleep, feel very sleepy during the day despite enough time in bed, regularly struggle to fall or stay asleep, or act out your dreams by shouting, kicking or punching in your sleep. These can be signs of sleep apnea, insomnia or REM sleep behavior disorder, and a sleep study can measure your stages properly.

For practical ways to protect your REM sleep, see our guide to how to increase REM sleep.

Frequently Asked Questions

How many stages of sleep are there?

Four: three stages of non-REM sleep (N1, N2 and N3) and REM sleep (Patel and colleagues, 2024).

What are the 4 stages of sleep in order?

A cycle usually runs N1, N2, N3 (deep sleep), back to N2, then REM, and repeats four to five times a night (Patel and colleagues, 2024).

Is REM sleep deep sleep?

No. Deep sleep is N3, a non-REM stage; REM is a separate stage with active, wake-like brain waves (Patel and colleagues, 2024).

How long is one sleep cycle?

Roughly 90 to 110 minutes (Patel and colleagues, 2024).

What is core sleep?

A tracker label for light sleep, meaning stages N1 and N2. Tracker stage estimates are less accurate than a sleep lab (Chinoy and colleagues, 2021).

How much of each sleep stage is normal?

In young adults, roughly 5% N1, 45% N2, 25% N3 and 25% REM (Patel and colleagues, 2024); deep and REM sleep shares fall with age (Ohayon and colleagues, 2004).

Do you only dream in REM sleep?

No. Dreams are most vivid in REM, but people also report dreams when woken from non-REM sleep (Siclari and colleagues, 2017).

Does alcohol affect sleep stages?

Yes. It delays the first REM period, lowers total REM at moderate and high doses, and disrupts the second half of the night (Ebrahim and colleagues, 2013).