Depending on their age, a person needs 7–17 hours sleep in every 24 hours. But, just sleeping is not enough. Deep sleep is essential for health and wellbeing. Most adults need around 1.5–2 hours of deep sleep per night.

The Centers for Disease Control and Prevention (CDC) advise adults aged 18–60 years to aim for at least 7 hours of sleep per night. Around 25% of this should be deep sleep.

Sleep happens in stages, and we spend different lengths of time in light and deep sleep. All the stages are important, but they serve different purposes.

Here, learn about the stages of sleep, what deep sleep is, and how much you need.

Here are some key facts about the stages of sleep:

  • People go through two types of sleep in each cycle:
    • one stage of rapid eye movement (REM) and
    • three stages of non-rapid eye movement (NREM)
  • NREM is divided into three stages:
    • light (N1)
    • deep (N2)
    • deeper sleep (N3)
  • A person cycles through these stages 4–5 times every night.
  • The stages cycle in this order: N1, N2, N3, N2, REM.
  • Each cycle lasts around 90–110 minutes.
  • The first REM stage is short, but as sleep progresses it gets longer compared with NREM.

The table below gives some details about the stages of sleep.

StageREM or non-REM (NREM)% of sleepAround how many minutes?Characteristics
Wake/alertThe person is relaxed. This stage lasts from when the eyes are open to when the person becomes drowsy and their eyes close.
N1 (NREM stage 1): Lighter sleepNREM5%1–5 minutesThe person is asleep but their skeletal muscle tone and breathing is the same as when awake.
N2 (NREM stage 2): Deeper sleepNREM45%25 minutes in first cycleThe length of this stage increases with each cycle. Bruxism (teeth grinding) may occur.
N3 (NREM stage 3): Deepest non-REM sleepNREM25%105 minutes in total, shared between cyclesThe deepest stage of sleep, this is when the body repairs and regrows tissues, builds bone and muscle, and strengthens the immune system. Sleepwalking, night terrors, and bedwetting may occur. A person is hard to wake. If they are woken at this stage, they may feel groggy for 30–60 minutes after.
REM sleep
25%10 minutes in first cycle, increasing with each cycle.Associated with dreaming, REM is not restful sleep. Eyes and breathing muscles are active but skeletal muscles are paralyzed. Breathing may be irregular and erratic. Usually follows the other stages, starting around 90 minutes after falling asleep.

In healthy adults, about 70% of sleep is deep sleep and around 25% of your sleeping time is your deepest sleep. So, if you sleep for 7–8 hours, the time spent in your deepest sleep should be around 105–120 minutes or one and three quarters to 2 hours.

However, as you get older, you’ll need less of this very deep sleep and spend more time in N2.

During the deepest sleep, a variety of functions take place, including:

  • relaxation of muscles
  • increase in blood supply to the muscles
  • slowing of heart rate and breathing
  • tissue growth and repair
  • release of essential hormones

Without deep sleep, these functions cannot take place and you may start to experience the symptoms of sleep deprivation.

How much REM sleep do you need?

There’s no official agreement on how much REM sleep you need, but this stage is important for dreaming, and experts believe dreaming helps you process emotions.

For most adults, REM takes up about 25% of sleep, which seems to be healthy during average sleep cycles.

How much light sleep do you need?

There is no minimum requirement for light sleep. It is nearly impossible to avoid light sleep if you want to sleep.

How much deep and light sleep do children need?

Babies and children need more sleep than adults. Newborns need the most, around 14–17 hours in every 24 hours.

This includes:

  • quiet sleep, which is similar to NREM sleep
  • active sleep, similar to REM sleep
  • indeterminate sleep

They go through only one or two cycles in every period of sleep.

As children grow older, the amount of total sleep they need decreases.

Here are the CDC’s recommendations for sleep in children:

AgeSleep requirements per 24 hours
0–3 months14–17 hours, with the longest episode lasting 2.5–4 hours
4–12 months12–16 hours, with naps
1–2 years11–14 hours, with naps
3–5 years10–13 hours, with naps
6–12 years9-12 hours
13–18 years8–10 hours

Signs that children are having sleep problems include:

  • irritability
  • learning and memory problems
  • frequent illness

However, it is not yet clear what proportion of deep, light, and REM sleep children and teens need at each stage.

People may not get enough deep sleep if they:

  • don’t sleep long enough
  • sleep but toss and turn all night
  • work shifts and sleep in the day or have changing sleep patterns
  • have jet lag or frequently travel between time zones
  • have a health condition that affects their ability to sleep

You can’t force your brain to go into deep sleep, but various strategies may help you get the right amount of quality sleep.

These include:

  • practicing strategies to manage stress
  • establishing sleep routines, such as a bath before bed
  • sleeping in a quiet, darkened room with a comfortable temperature
  • using an eye mask to block out light
  • exercising for 20–30 minutes during the day but not within the last few hours before bedtime
  • avoiding large meals, caffeine, nicotine, and alcohol close to bedtime
  • doing relaxation exercises or meditation
  • getting up and doing something, such as reading, if you can’t sleep
  • leaving distractions, such as phones and other devices, outside the room

A range of sleep trackers may help you track your sleep patterns and see how much light, REM, and deep sleep you are getting.

For more sleep support, check out our sleep shop.

If you’re aged 18–60 and are sleeping for 7–8 hours per night but are not waking up feeling refreshed, you may not be getting enough deep sleep.

You might want to ask a doctor about doing a sleep study to help you figure our your sleep patterns. You may need treatment for a sleep disorder.

Possible causes of sleep disturbances include:

  • obstructive sleep apnea
  • pain or other symptoms that can affect sleep
  • REM sleep disorder
  • narcolepsy
  • a mental health condition, such as depression or anxiety
  • older age
  • dementia
  • traumatic brain injury
  • the use of some medications

You may be feeling tired because you are not getting enough sleep or getting too much sleep.

Quality sleep is as important to health as food and water.

It supports functions such as:

  • the immune system and resistance to disease
  • healthy metabolism
  • brain, heart, and lung function
  • mood

A lack of quality sleep may increase the risk of:

  • obesity
  • high blood pressure
  • type 2 diabetes
  • cardiovascular disease
  • depression

Is 45 minutes of deep sleep enough?

An adult aged 18–60 years needs 7 or more hours of sleep in every 24 hours. Around 25% or 105 minutes of this is typically the deepest sleep. In which case, a total of 45 minutes is not enough deep sleep.

However, sleep goes in cycles, so a person may not have 105 minutes of the deepest sleep all in one stage.

What happens if you don’t get the right amount of deep sleep?

In your deepest sleep, your body repairs and regrows tissues, builds bone and muscle, and strengthens the immune system.

If you don’t get enough deep sleep, you may be more prone to physical and mental health issues, as well as feeling sleepy during the day.

How do I increase my amount of deep sleep?

There is no way to make yourself sleep deeper, but you can increase your chances of sleeping well if you follow some tips, such as:

  • establishing regular sleep-wake habits, including getting up and going to bed at the same time every day
  • ensuring your sleeping space is as quiet, comfortable, and restful as possible
  • leaving any devices outside the room while you sleep
  • establishing a bedtime routine that helps you relax before sleep, such as having a warm shower or listening to music

Which is better, REM or deep sleep?

All the stages of sleep are necessary, and none is better than any other. You need a balance of around 25% REM and 25% of the deepest NREM sleep to maintain your health and wellbeing.

Getting the right balance of sleep in each stage is essential to health. The five stages of sleep involve light NREM sleep, deep NREM sleep, and REM sleep.

REM sleep is when we tend to dream, and the deepest NREM sleep is when the body relaxes fully and repairs itself.

The amount of sleep we need varies by age, but the CDC recommend at least 7 hours of sleep in every 24 hours for adults. In addition, getting around 1.5–2 hours of deep sleep is crucial for feeling rested and staying healthy.

If you’re having trouble with sleep and wakefulness, it’s best to speak with a doctor, as good quality sleep is essential for health and wellbeing.