Most adults need roughly 1.5 to 2 hours each of deep sleep and REM sleep per night, assuming a total of 7 to 9 hours in bed. Deep sleep should make up about 20 to 25% of your total sleep time, and REM sleep accounts for another 25%. That translates to approximately 60 to 120 minutes of each stage during a full night’s rest.
How Much Deep Sleep You Need
Adults should aim for about 60 to 100 minutes of deep sleep during an 8-hour night. Deep sleep (also called stage 3 or slow-wave sleep) is the physically restorative phase. Your body releases a surge of growth hormone during this stage, which drives protein synthesis, muscle and bone repair, and helps regulate how your body processes fat and glucose. This is the sleep that makes you feel physically recovered the next day.
Deep sleep is heaviest in the first half of the night. During your earliest sleep cycles, deep sleep stages typically last 20 to 40 minutes each. As the night progresses, those deep sleep windows shrink and eventually give way to longer periods of REM. This is why cutting your sleep short by even an hour or two doesn’t cost you much deep sleep but can significantly reduce your REM time.
How Much REM Sleep You Need
REM sleep also accounts for about 25% of total sleep time, or roughly 90 to 120 minutes per night. Unlike deep sleep, REM periods are short early in the night and grow longer toward morning. You typically don’t enter your first REM period until about 90 minutes after falling asleep, and the longest REM stretches happen in the final hours before waking.
REM sleep serves your brain the way deep sleep serves your body. During REM, your brain consolidates emotional memories, strengthening the factual content of experiences while stripping away the raw emotional charge attached to them. Researchers at UC Berkeley have described this as a kind of “overnight therapy”: your brain replays emotionally significant events in a neurochemical environment free of stress chemicals, allowing you to retain the lesson without re-experiencing the full intensity of the feeling. This is why a bad day often feels more manageable after a full night’s sleep.
Sleep deprivation hits REM-dependent functions hard. Even one night of poor sleep amplifies the brain’s emotional reactivity to negative experiences and weakens the connection between the emotional centers of the brain and the regions responsible for rational control. Over time, consistently short REM sleep is linked to difficulty with emotional regulation, problem-solving, and learning.
How Sleep Stages Shift Through the Night
Your body doesn’t distribute deep sleep and REM evenly. A typical night runs through four to six sleep cycles, each lasting about 90 minutes, but the composition of those cycles changes as the night goes on.
In the first two cycles, deep sleep dominates. This is your body’s priority: physical repair first. By the third and fourth cycles, deep sleep periods shrink to just a few minutes or disappear entirely, and REM takes over. Your longest, most vivid dream periods happen in the last cycle or two before your alarm goes off. This architecture explains a few common experiences: waking up very early (say, after five hours) often leaves you physically rested but mentally foggy, because you got most of your deep sleep but missed the bulk of your REM. Sleeping in on weekends, on the other hand, primarily adds REM time.
What Affects Your Deep and REM Sleep
Age is the biggest factor. Deep sleep declines steadily from your 20s onward. By middle age, many people get half the deep sleep they did as teenagers, even if total sleep time stays the same. REM sleep is more stable across the lifespan but still decreases somewhat with age.
Alcohol is one of the most common disruptors. It increases deep sleep in the first half of the night but suppresses REM sleep dramatically, especially in the second half. This is why you can sleep a full eight hours after drinking and still wake up feeling mentally dull. Caffeine consumed within six hours of bedtime reduces deep sleep. And irregular sleep schedules, where your bedtime shifts by more than an hour from night to night, can fragment both stages.
Exercise reliably increases deep sleep, particularly moderate aerobic activity done earlier in the day. Temperature matters too: your body needs to cool down slightly to enter deep sleep, so a warm bedroom or heavy bedding can reduce time spent in that stage.
How Accurate Your Sleep Tracker Really Is
If you’re checking your deep and REM numbers on a wearable device, take the specific stage breakdowns with a grain of salt. A study comparing three popular wearables (Oura Ring, Fitbit, and Apple Watch) against polysomnography, the gold-standard sleep lab test, found that all three devices had poor agreement with clinical measurements for both deep and REM sleep specifically. The statistical concordance scores for deep and REM sleep ranged from just 0.13 to 0.37, which is considered poor reliability.
The details varied by device. The Oura Ring came closest to clinical measurements overall and didn’t significantly over- or underestimate any sleep stage. Fitbit underestimated deep sleep by about 15 minutes per night. The Apple Watch underestimated deep sleep by a striking 43 minutes per night, meaning if it shows you got 45 minutes of deep sleep, the real number could be closer to 90. Sensitivity for detecting individual deep sleep epochs ranged from just 50% (Apple Watch) to about 80% (Oura Ring).
Wearables are reasonably good at tracking total sleep time and sleep efficiency. They’re useful for spotting trends, like noticing that your deep sleep drops on nights you drink alcohol or go to bed late. But obsessing over whether you got 58 or 72 minutes of deep sleep on a given night isn’t productive, because the device simply isn’t precise enough at that level. If your tracker consistently shows very low amounts of a particular stage over weeks, that pattern is worth paying attention to, even if the exact numbers are off.
Signs You’re Not Getting Enough
Because deep sleep and REM sleep serve different functions, their deficits feel different. Too little deep sleep tends to show up as physical symptoms: persistent muscle soreness, slow recovery from workouts, feeling physically heavy or unrested even after a long night. You might also get sick more frequently, since deep sleep supports immune function.
Too little REM sleep shows up cognitively and emotionally. You may notice difficulty concentrating, trouble recalling details, or a shorter emotional fuse. Small frustrations feel bigger than they should. Creative problem-solving suffers. If you’re sleeping enough hours but still feel mentally foggy and emotionally reactive, fragmented REM is a likely culprit, often caused by alcohol, sleep apnea, or frequent nighttime awakenings.
The practical takeaway is straightforward: consistently sleeping 7 to 9 hours on a regular schedule, in a cool and dark room, without alcohol close to bedtime, gives your body the best chance of cycling through enough deep and REM sleep naturally. Your brain already knows how to allocate these stages. The main job is giving it enough uninterrupted time to do so.