Deep Sleep vs REM Sleep: Differences, How Much You Need & How to Improve Sleep

Deep sleep and REM sleep are often treated as though they are competing scores.

Your sleep tracker may tell you that you got 52 minutes of deep sleep and 1 hour 47 minutes of REM, leaving you wondering which number matters more — and whether one of them is too low.

But deep sleep and REM sleep are not interchangeable versions of “good sleep.”

They are biologically different stages that occur as part of the normal sleep cycle, and the amount of each naturally changes across the night.

There is also an important misconception worth clearing up:

Deep sleep is not simply “for the body” while REM sleep is “for the brain.” Healthy sleep is more interconnected than that, and both stages contribute to normal sleep function.

Quick Answer

Deep sleep and REM sleep are different stages of normal sleep, and neither is universally more important than the other.

Deep sleep is stage N3, the deepest stage of non-REM sleep. It is characterized by slow, high-amplitude brain waves and is concentrated more heavily during the earlier part of the night.

REM stands for rapid eye movement. During REM sleep, brain activity becomes more similar in some ways to wakefulness, rapid eye movements occur and most skeletal muscles become temporarily inactive. REM periods generally become longer later in the night.

Reference descriptions of healthy adult sleep often place N3 deep sleep at roughly 20% of total sleep and REM at roughly 20% to 25%, but those numbers are not targets that every person must hit every night.

Deep Sleep vs. REM Sleep: What Is the Difference?

The simplest distinction is that deep sleep and REM are separate stages with very different physiological patterns.

Those percentages are useful for understanding general sleep architecture, but they should not become nightly goals.

Age, total sleep duration, recent sleep loss, medications, alcohol, health conditions and normal night-to-night variation can all affect stage distribution.

What Is Deep Sleep?

Deep sleep is stage N3 of non-REM sleep.

It is also called slow-wave sleep because of the large, slow electrical waves observed when brain activity is measured during polysomnography.

The National Heart, Lung, and Blood Institute describes N3 as the deepest stage of non-REM sleep and notes that people generally spend more time in it earlier in the night.

The National Institute of Neurological Disorders and Stroke similarly describes stage 3 as occurring in longer periods during the first half of the night.

During N3, heartbeat and breathing slow, muscles are relaxed and it is generally more difficult to wake someone than during lighter stages of sleep.

If you are awakened abruptly from deep sleep, you may also experience temporary grogginess or mental fogginess sometimes called sleep inertia.

What Is REM Sleep?

REM stands for rapid eye movement.

REM is a distinct phase of sleep rather than another level of non-REM sleep.

During REM, the eyes move rapidly behind closed eyelids and brain activity becomes relatively active compared with deep sleep.

Breathing and heart rate can also become more variable.

At the same time, most skeletal muscles become temporarily inactive, which helps prevent you from physically acting out normal REM dreams.

Dreaming can occur during several stages of sleep, but vivid dreaming is particularly associated with REM.

REM sleep begins during the earlier portion of the night, but the periods generally become progressively longer as morning approaches.

For the broader picture of how all four stages — N1, N2, N3 and REM — repeat through the night, see our guide to sleep cycle stages, length and normal overnight sleep architecture.

Do Deep Sleep and REM Sleep Do Different Things?

Yes, but the difference should not be reduced to a simple slogan.

You may see claims online that:

“Deep sleep restores the body, while REM restores the brain.”

That is too simplistic.

Different sleep stages are associated with different physiological and neurological processes, but sleep functions overlap and interact.

For example, sleep is important for learning and memory, and evidence does not support assigning memory exclusively to REM sleep.

A 2024 systematic review and meta-analysis examining sleep restriction and memory formation found results consistent with complementary roles for slow-wave sleep and REM sleep.

The NINDS also notes that memory consolidation most likely requires both non-REM and REM sleep.

So a better way to think about the stages is:

Deep sleep and REM have different physiological characteristics, but healthy sleep depends on the complete architecture rather than choosing one “best” stage.

When Do Deep Sleep and REM Happen During the Night?

Deep sleep and REM are not evenly distributed from bedtime until morning.

Earlier in the Night: More Deep Sleep

The first several sleep cycles contain a greater concentration of N3 deep sleep.

This means the first part of the night generally contains longer periods of slow-wave sleep than the later part.

Later in the Night: More REM

As the night continues, deep N3 sleep generally decreases.

REM periods become progressively longer and make up a larger portion of later sleep cycles.

This is one reason cutting several hours from the end of your normal sleep period does not simply remove “extra” sleep. It can disproportionately reduce later-night REM opportunity.

The change from more deep sleep early to more REM later is part of normal sleep architecture.

Which Is More Important: Deep Sleep or REM Sleep?

Neither should be treated as universally more important.

Asking whether deep sleep or REM is “better” is a little like asking whether one normal phase of a biological process should replace another.

Healthy sleep naturally includes both.

N3 and REM have different patterns of brain activity, muscle tone and physiology, and the body regulates their distribution across repeated sleep cycles.

You also do not normally choose how much time to spend in either stage.

Your brain regulates sleep architecture based on interacting biological factors including sleep pressure, circadian timing, prior sleep, age and health.

That makes total sleep opportunity and continuity more useful goals than trying to maximize one stage at the expense of another.

How Much Deep Sleep Do You Need?

There is no universal number of minutes of deep sleep that every adult must obtain each night.

Reference descriptions of adult sleep staging commonly place N3 at roughly 20% of total sleep.

For someone sleeping eight hours, 20% would mathematically equal about 96 minutes.

But that does not mean 96 minutes is a clinical target or that getting less on one night indicates a problem.

The percentage of deep sleep varies between people and changes substantially across adulthood.

It also depends on how total sleep time is measured.

A consumer wearable saying you received exactly 73 minutes of deep sleep is giving you an estimate, not the same measurement you would receive from laboratory polysomnography.

How Much REM Sleep Do You Need?

REM sleep is commonly described as accounting for roughly 20% to 25% of total sleep in adults.

Again, that is a population-level reference range rather than a nightly score everyone must achieve.

If someone slept eight hours, 20% to 25% would correspond mathematically to about 96 to 120 minutes.

But an individual night can fall outside that range without proving that anything is wrong.

The amount of REM you obtain can be influenced by total sleep duration, when during the night you sleep, recent sleep patterns, medications, alcohol, health conditions and other factors.

Because REM periods become longer later in the night, routinely shortening the latter portion of your sleep opportunity may also affect how much REM sleep you have the opportunity to obtain.

How Do Deep Sleep and REM Change With Age?

Sleep architecture changes across adulthood.

One of the more consistent age-related changes is a reduction in slow-wave or N3 deep sleep.

A 2022 review of sleep in normal aging describes decreased slow-wave sleep, more nighttime awakenings and more time awake during the night as common age-related patterns.

Importantly, the review notes that many measurable changes occur between young and middle adulthood rather than suddenly beginning only in old age.

That matters for adults in their 40s, 50s and beyond who compare current tracker results with how they remember sleeping in their 20s.

A lower amount of deep sleep with age does not automatically mean your sleep is unhealthy.

REM can also change across the lifespan, but individual variation is substantial and wearable stage estimates make precise personal comparisons difficult.

Age-related change also does not mean persistent sleep disruption should simply be dismissed as “getting older.”

What Does Low Deep Sleep Mean?

A low deep-sleep number on one night does not provide a diagnosis.

Before interpreting the number, consider several questions:

• Was your total sleep time shorter than usual?
• Was your sleep repeatedly interrupted?
• Did you drink alcohol?
• Were you sick, stressed or sleeping in an unusual environment?
• Is the result coming from a wearable rather than polysomnography?
• Is this one unusual night or a consistent pattern?
• Do you actually have daytime symptoms?

The number deserves more attention when it is part of a larger persistent sleep problem rather than an isolated tracker result.

What Does Low REM Sleep Mean?

The same caution applies to a low REM reading.

A wearable estimating less REM than usual does not tell you why the number changed or establish that you have a REM-related disorder.

Total sleep duration is particularly relevant because more REM generally occurs later in the sleep period.

If you regularly cut your sleep short, there may simply be less opportunity for the longer REM periods that tend to occur toward morning.

Medications, alcohol, sleep disruption and other physiological factors can also alter sleep architecture.

Again, the broader pattern matters more than one colored section of a nightly graph.

Can Apple Watch, Oura or Fitbit Accurately Measure Deep and REM Sleep?

Consumer sleep trackers can be useful, but their sleep-stage graphs look more precise than the underlying measurement actually is.

Clinical sleep staging is performed using polysomnography, which records signals including brain activity, eye movements and muscle activity.

Consumer watches and rings do not directly reproduce that laboratory measurement.

Instead, they use available signals such as movement, heart-rate patterns and other physiological measurements to estimate when different sleep stages occurred.

A 2026 systematic review and meta-analysis comparing wearable sleep trackers with polysomnography found that wearables can provide reasonable estimates of broad sleep metrics and may be useful for longitudinal self-tracking.

However, performance varied considerably between devices, and the researchers concluded that current wearables should not be treated as stand-alone diagnostic tools or as equivalent to polysomnography for detailed sleep-stage characterization.

So if your device reports:

Deep: 54 minutes
REM: 1 hour 36 minutes

it is more defensible to interpret those numbers as estimates within a pattern than as exact laboratory measurements.

If your Apple Watch also shows a large amount of Core sleep, remember that Apple uses Core as its label for estimated N1 and N2 non-REM sleep. Our guide to what Core Sleep means on Apple Watch explains why that terminology can be confusing.

Can You Increase Deep Sleep or REM Sleep?

Trying to directly manipulate one sleep stage is usually the wrong starting point.

You do not consciously choose when your brain enters N3 or REM.

A more defensible goal is to support the conditions that allow normal sleep architecture to unfold.

That means focusing on fundamentals such as:

• allowing adequate opportunity for sleep
• keeping sleep and wake timing reasonably consistent
• getting daytime light and physical activity
• paying attention to caffeine and alcohol timing
• reducing avoidable nighttime disruption
• keeping the bedroom dark, quiet and comfortable
• addressing persistent symptoms or an underlying sleep disorder

For a practical framework covering those habits, see our Sleep Hygiene Checklist and guide to improving sleep habits.

The objective is not to “hack” your graph until one color gets larger.

It is to support sufficient, reasonably continuous sleep and address whatever is repeatedly disrupting it.

When Should You Talk With a Healthcare Professional?

A tracker showing less deep or REM sleep than you expected is not, by itself, a reason to assume you have a sleep disorder.

Consider professional evaluation when sleep concerns occur alongside symptoms such as:

• persistent difficulty falling asleep or staying asleep
• repeated nighttime awakenings
• significant daytime sleepiness
• persistent fatigue despite adequate opportunity for sleep
• loud snoring
• gasping or choking during sleep
• witnessed pauses in breathing
• frequent morning headaches
• sleep problems that interfere with driving, work or normal daily functioning

The key distinction is between being concerned about a number on a device and experiencing a persistent sleep or daytime-function problem.

The second deserves more attention than the first.

Frequently Asked Questions

What is the difference between deep sleep and REM sleep?

Deep sleep is stage N3 of non-REM sleep and is characterized by slow-wave brain activity, reduced heart rate and breathing and a high threshold for awakening. REM is a separate sleep phase characterized by rapid eye movements, relatively active brain activity and temporary loss of most skeletal muscle tone.

Which is better, REM or deep sleep?

Neither is universally better. Deep sleep and REM are different parts of normal sleep architecture, and healthy sleep includes both. Trying to maximize one at the expense of the other is not a useful goal.

How much deep sleep should an adult get?

Reference descriptions of healthy adult sleep often place N3 deep sleep at approximately 20% of total sleep. This is a population reference value rather than a target that every person needs to reach each night, and deep sleep generally decreases with age.

How much REM sleep should an adult get?

REM commonly accounts for roughly 20% to 25% of adult sleep in reference descriptions. Individual nights vary, and wearable estimates should not be interpreted as exact clinical measurements.

Is deep sleep the same as REM sleep?

No. Deep sleep is N3 non-REM sleep. REM is a separate phase with different patterns of brain activity, eye movement and muscle tone.

Does deep sleep happen before REM?

During a typical sleep cycle, sleep progresses through non-REM stages before reaching REM. Deep N3 sleep is concentrated more heavily in earlier cycles, while REM periods generally become longer later in the night.

Is REM sleep deeper than deep sleep?

No. The term deep sleep specifically refers to N3, the deepest non-REM stage. REM is physiologically distinct and has relatively active brain activity despite the person remaining asleep.

Why am I getting more REM than deep sleep?

That can be completely normal, particularly because deep sleep decreases with age and REM is concentrated more heavily in later sleep cycles. Consumer trackers also estimate rather than directly measure sleep stages, so one night's ratio should be interpreted cautiously.

Why am I getting more deep sleep than REM?

Sleep-stage proportions vary between people and nights. Total sleep duration, sleep timing, recent sleep loss, age, alcohol, medications and tracker-estimation error can all influence the apparent balance. One night alone usually does not provide enough information to identify a problem.

Can a sleep tracker tell if I am in REM or deep sleep?

Consumer trackers estimate sleep stages using signals available to the device. They can be useful for observing trends over time, but they are not equivalent to polysomnography and should not be treated as exact sleep-stage measurements or diagnostic tools.

Can I increase my deep sleep?

You cannot directly choose to enter N3 sleep. A more useful approach is to allow adequate sleep opportunity, keep reasonably consistent timing, reduce factors that fragment sleep and address persistent sleep problems rather than trying to force one stage to increase.

Can I increase my REM sleep?

REM is regulated as part of normal sleep architecture. Because REM periods become longer later in the night, allowing enough total sleep opportunity is particularly important. Rather than trying to manipulate REM directly, focus on supporting healthy sleep overall.

The Bottom Line

Deep sleep and REM sleep are not competitors.

Deep sleep is N3, the deepest stage of non-REM sleep, and is concentrated more heavily during the first part of the night.

REM is a distinct phase characterized by rapid eye movements, active brain patterns and temporary muscle atonia, and its periods become progressively longer later in the night.

Reference descriptions often place adult N3 around 20% of total sleep and REM around 20% to 25%, but those numbers should be treated as broad context rather than nightly targets.

Age, total sleep duration, health, recent sleep, medications and normal biological variation all affect sleep architecture — and consumer trackers add another layer of estimation.

Instead of trying to maximize one stage, focus on the larger pattern: whether you allow enough time for sleep, whether your sleep is reasonably continuous, how you feel during the day and whether persistent symptoms suggest that something is disrupting your sleep.

Sources and Further Reading

• National Heart, Lung, and Blood Institute — Sleep Phases and Stages
• National Institute of Neurological Disorders and Stroke — Understanding Sleep
• National Library of Medicine — Sleep Staging and EEG Wave Frequency
• Systematic and Meta-Analytic Review of Sleep Restriction and Memory Formation
• Li J, Vitiello MV, Gooneratne NS. Sleep in Normal Aging. Sleep Medicine Clinics. 2022.
• Are Wearable Sleep-Tracking Devices Reliable Alternatives to Polysomnography? A Systematic Review and Meta-Analysis. 2026.

This article is provided for educational purposes only and is not intended to diagnose, treat, cure or prevent any disease or replace individualized medical advice.