Sleep Cycles Stages Explained: Light, Deep, REM & Wake

Sleep is a dynamic process. The average healthy adult will experience 4-6 sleep cycles per night, with four distinct sleep stages: Light Sleep, Deep/Slow Wave Sleep (SWS), Rapid Eye Movement (REM) Sleep, and Wake.

What is a sleep cycle

A sleep cycle is the progression through the different stages of sleep, from light sleep to deep sleep, then REM, and finally a brief awakening. Each full cycle lasts about 90 minutes on average, and you will typically experience four to six of these cycles per night.

The composition of each cycle changes as the night goes on — you get more deep sleep earlier in the night and more REM sleep closer to when you wake up. Understanding these cycles is the key to interpreting your sleep quality and its impact on your daily performance.

The four stages of sleep

Light sleep represents the physiological process taken to transition to deep sleep. Some of the restorative characteristics that define deep sleep occur in this phase, but with less frequency, as your body is more responsive to your environment. There is a theory that light sleep exists to allow the body to be aware of its surroundings and to wake quickly in the event of a threat.

Slow Wave Sleep (SWS), also known as deep sleep, is the time when your muscles repair and grow. During this stage the body produces 95% of its daily supply of growth hormones. Training sessions break down muscle tissue so that it can rebuild and grow during slow wave sleep.

REM sleep is when the brain is restored. It is at this time that ideas and skills acquired during the day are cemented as memories. Any time you are practicing a technical skill, the actual consolidation and retention of that learning happens during REM sleep.

Wake is included as a sleep stage because it is natural to be awake for brief periods many times in the night. These periods are known as arousals, or "disturbances" in the WHOOP app, and it is normal to experience anywhere from 10-20 per night. While they only last a few minutes and you're not conscious of them, you can lose upwards of an hour of sleep in the Wake stage due to disturbances.

How sleep cycles progress through the night

Sleep is entered through light sleep, transitions to SWS within about 10 minutes, then to REM sleep somewhere around 90 minutes after falling asleep. An arousal will follow and a new sleep cycle will begin from there. A normal night of sleep will contain 3-5 complete cycles, with more possible the longer you sleep.

How much time should you spend in each stage of sleep

The amount of time a person will spend in each sleep stage varies night by night. In general, a healthy break down to aim for is the following:

• 50% Light
• 22% REM
• 23% SWS (Deep)
• 5% Awake

Analyzing your sleep stages and trends with WHOOP

The sleep trends accessible on the WHOOP App give you the opportunity to unpack nighttime habits that either help or hurt your sleep efficiency. You can see your restorative sleep trends (your combined deep and slow wave sleep) over time for a closer look at how much you're getting and when. Looking for patterns like this can help you build routines that maximize your WHOOP recovery and improve your heart rate variability, one of the key metrics for determining your body's readiness to perform each day.

Tips for improving your sleep cycles

While there is no simple formula for boosting the amount of time you spend in any of the stages of sleep, there are behaviors you can adopt to give yourself the best chance at an efficient night of sleep. Here are some good practices we've learned from the leading studies on sleep science:

• The darker your room, the better you sleep. Light influences the wake stage of sleep so the darker you can get your room, the more time you will get in the restorative stages.
• Set your room temperature at or around 68 degrees. You will fall asleep quicker when your bedroom is slightly cool.
• Your bed is not a multi-use space. The more you can train your body to associate your bed with sleep, the more adept you will be at falling asleep in that space. Avoid work and leisure time spent in your bed.
• Screens are stimulating and keep you awake. Avoid using your phone or computer in bed, as screen time makes it more difficult to fall asleep.
• Set a cut-off time for caffeine intake. Caffeine has a lingering presence for many hours after consumption. For greater sleep efficiency, consciously refrain from caffeine consumption at least 4 hours before bed.
• Plan ahead when consuming alcohol. Just as caffeine intake impacts the body hours after consumption, so too does alcohol. Keep this in mind on a night out so that your sleep performance doesn't suffer.
• Fall asleep and wake up at similar times each day. We call this sleep consistency, and studies have shown it can improve the quality and efficiency of your time in bed.
• Listen to the WHOOP Sleep Planner. Based on your physiological data and natural circadian rhythm, the Sleep Planner makes daily recommendations for your optimal time to go to bed at night and get up the next morning.

Understand your sleep to unlock your potential

Understanding your unique sleep architecture is the first step toward improving it. When you can see how your behaviors impact your time in each sleep stage, you can make targeted changes that enhance your nightly recovery.

Frequently asked questions about sleep stages

Is it better to get more REM or deep sleep?

Both deep sleep and REM sleep are critical for recovery, but they serve different functions. Deep sleep is primarily for physical restoration — repairing muscles, strengthening your immune system, and cellular regeneration. REM sleep is for mental restoration, including memory consolidation and learning.

A healthy night of sleep contains a balance of both. Rather than aiming for more of one over the other, the goal is to get enough of each to feel fully restored.

Why do I get more deep sleep at the beginning of the night?

Your body prioritizes physical restoration first. The majority of your deep sleep occurs in the first half of the night, during the first few sleep cycles. This is when your body focuses on repairing itself from the day's strain.

As the night progresses, sleep cycles shift to prioritize REM sleep, which is essential for cognitive function and mental recovery.

What is the 10-3-2-1-0 rule for better sleep?

The 10-3-2-1-0 rule is a simple guideline to help prepare your body for sleep. It stands for: 10 hours before bed, no more caffeine. 3 hours before bed, no more large meals or alcohol.

2 hours before bed, no more work. 1 hour before bed, no more screen time. And 0 is the number of times you hit the snooze button in the morning.

Can I control which sleep stage I get more of?

While you can't directly control which sleep stage you enter, you can influence the amount of time you spend in them through your daily behaviors. For example, intense exercise during the day can increase your body's need for deep sleep to repair muscles. Engaging in mentally stimulating activities or learning new skills can promote more REM sleep.