Most healthy adults need about 90 to 120 minutes of REM sleep and 60 to 100 minutes of deep sleep per night, assuming a total of seven to nine hours in bed. Those two stages make up a relatively small fraction of your overall sleep, but they carry outsized importance for your brain, immune system, and long-term health.
Deep Sleep: How Much You Need
Deep sleep, also called slow-wave sleep or Stage 3, should account for roughly 10% to 20% of your total sleep time. For someone sleeping seven hours, that translates to about 42 to 84 minutes. For eight hours of sleep, the range is 48 to 96 minutes. Stony Brook Medicine puts the practical target at approximately 60 to 100 minutes per night for adults getting a full eight hours.
During deep sleep, your brain produces slow, powerful electrical waves and your body shifts into its most restorative state. This is when tissue repair accelerates, the immune system strengthens, and growth hormone is released in its largest pulse of the day. If you’ve ever slept a full night but still felt physically run down, a shortage of deep sleep is one of the likeliest explanations. Your body simply didn’t get enough time in the stage where the heaviest repair work happens.
Most of your deep sleep is concentrated in the first half of the night, typically within the first two or three sleep cycles. That’s why going to bed very late or waking up frequently in the early hours can disproportionately cut into this stage, even if your total sleep time looks reasonable on paper.
REM Sleep: How Much You Need
REM sleep typically makes up 20% to 25% of total sleep in adults, which works out to roughly 90 to 120 minutes across a full night. Unlike deep sleep, REM periods get longer as the night goes on. Your first REM episode might last only 10 minutes, while later ones can stretch past 30 minutes. This back-loading means that cutting your night short by even an hour or two disproportionately reduces REM time.
REM sleep is when the brain is most active during sleep, nearly as active as when you’re awake. This stage plays a central role in memory processing, helping the brain sort through the day’s experiences, strengthen useful memories, and discard information it doesn’t need. Research from the National Institutes of Health suggests the brain uses REM sleep to actively forget excess or unimportant information, preventing mental overload. This pruning process may also explain why dreams, which occur primarily during REM, are so quickly forgotten after waking.
A large study covered by the National Heart, Lung, and Blood Institute found that for every 5% reduction in REM sleep, death rates from all causes increased by 13% to 17% in the populations studied, which included both middle-aged and older adults. That doesn’t mean a single bad night is dangerous, but a chronic pattern of reduced REM sleep carries real long-term risk.
How These Stages Change With Age
Newborns spend roughly half their sleep time in a precursor to REM sleep, reflecting the enormous amount of brain development happening in those early months. As children grow and their neural networks mature, NREM sleep (including deep sleep) gradually takes over a larger share of the night, while REM percentage slowly declines.
By adulthood, deep sleep begins its own long decline. People in their 20s and 30s typically hit the higher end of the 10% to 20% range, while adults over 60 often get noticeably less, sometimes falling below 10%. REM sleep is more resilient with age but still tends to decrease modestly. These shifts are a normal part of aging, though they help explain why older adults often feel their sleep is lighter or less refreshing than it used to be.
What Disrupts Deep and REM Sleep
Alcohol is one of the most common disruptors. Having a drink or two before bed may help you fall asleep faster, but it fragments your sleep cycles throughout the night. Your brain briefly wakes up repeatedly, sending you back to lighter sleep stages and cutting into both REM and deep sleep. Because REM dominates the second half of the night, and alcohol’s sedative effect wears off during that window, REM sleep takes a particularly heavy hit.
Bedroom temperature matters more than most people realize. A room that’s too warm disrupts the body’s natural temperature regulation, which is critical for staying in restorative sleep stages. Heat specifically interferes with REM sleep, while a cool environment helps stabilize it. Sleep specialists recommend keeping your bedroom between 60 and 67°F (15 to 19°C). Think of your bedroom as a cave: cool, dark, and quiet.
Other factors that can reduce your time in deep or REM sleep include caffeine consumed within six to eight hours of bedtime, inconsistent sleep schedules, chronic stress, and sleep disorders like sleep apnea that cause frequent micro-awakenings you may not even remember.
How to Tell If You’re Getting Enough
Unless you use a clinical sleep study (polysomnography), you can’t measure your sleep stages with perfect accuracy. Consumer wearables like smartwatches and fitness trackers estimate sleep stages using heart rate and movement data, and while they’re useful for spotting trends over time, their nightly numbers can be off by a meaningful margin. Don’t panic over a single night’s readout showing low deep sleep.
Better indicators come from how you feel. If you consistently wake up feeling unrefreshed despite sleeping seven or more hours, struggle with concentration or memory during the day, get sick more often than you’d expect, or feel emotionally reactive, you may not be spending enough time in deep or REM sleep, even if your total hours look fine. The quality of sleep matters just as much as the quantity, and quality is largely determined by how much time you spend in these two stages versus cycling through lighter sleep.
Practical Ways to Protect Both Stages
The most effective strategies target both deep and REM sleep simultaneously, because they share many of the same vulnerabilities. Keeping a consistent sleep and wake schedule, even on weekends, helps your brain cycle through all stages more efficiently. Regular physical activity, particularly moderate aerobic exercise, has been shown to increase deep sleep duration, though exercising within two to three hours of bedtime can have the opposite effect for some people.
Limiting alcohol, especially within three to four hours of sleep, preserves REM architecture. Keeping your room cool (60 to 67°F) supports both slow-wave and REM stability. Reducing screen exposure in the hour before bed helps your brain transition into sleep more smoothly, which protects the early deep sleep periods that are hardest to recover once lost. And perhaps most importantly, simply giving yourself enough total time in bed, at least seven hours for most adults, ensures your body has the opportunity to complete enough full sleep cycles to accumulate adequate time in every stage.