How Much Deep Sleep Do You Need?

Tell me if this sounds familiar: You go to bed intending to sleep at least seven hours so that you’re ready to start the next day bright and early. When your alarm goes off, you think, “Great, I got so much sleep,” only to find yourself yawning non-stop and fending off the urge to lie back down. What gives?

Well, optimum sleep is more than just the number of hours you get each night. It’s also a bit of a complicated puzzle involving sleep cycles and stages, each with its own purposes and benefits. And if you’re trying to boost the quality of your shuteye, looking at your deep sleep can be particularly beneficial to understand how it all fits together. But what defines this stage of rest, and how much deep sleep do you need?

What Is Deep Sleep?

Deep sleep is an important stage in the sleep cycle that’s key for keeping your mind and body in tip-top shape. But what does that entail exactly?

While you might be ready to check out when your head hits the pillow, the work is just beginning for your body and brain. From the time you declare lights out to hitting snooze on your alarm, your body will likely go through four to five (and sometimes six) sleep cycles, with each cycle lasting about 90 to 120 minutes, according to the Cleveland Clinic. 

Experts believe each sleep cycle has two phases: non-rapid eye movement (NREM), which has three stages, and rapid eye movement (REM), which has one stage, according to the National Institutes of Health (NIH). 

When you go to sleep, you’ll typically start at NREM stage 1, then move between NREM stages 2 and 3, and then cap off the process with REM sleep before starting a new cycle, per the Cleveland Clinic. That said, not everyone will move through this cycle in chronological order, and some people may skip a stage or two, according to the Mayo Clinic. That’s what makes sleep so individual.  

Deep sleep (NREM stage 3), which is what we’re focused on here, is also called slow-wave sleep because of the characteristically slower delta brain waves. You’ll typically spend more time in this restorative sleep stage earlier in the night, per the NIH.

During deep sleep, your heart and respiratory rates are slow and your muscles are relaxed, allowing you to benefit from restorative snoozing that’s necessary for overall health. This state of deep relaxation is also why it’s difficult to wake someone up during deep sleep.

Why Is Deep Sleep Important?

During deep sleep, the body undergoes significant physical repair and restoration, including muscle recovery, tissue growth, and the release of growth hormones. It’s also the stage where your brain processes and consolidates information and experiences from the day, helping you retain and make sense of new things. 

What’s more, getting sufficient deep sleep can help your body fend off infections and illnesses, replenish energy reserves, and help you wake up feeling refreshed, energized, and ready to take on the day. 

How Much Deep Sleep Do You Need?

Deep sleep makes up about 25 percent of the total sleep time for adults. If you get the recommended seven to nine hours of shuteye each evening, your time spent in deep sleep would, in theory, translate to roughly one to two hours a night.

But there’s some major nuance to that number. Even if you get those recommended seven to nine hours, it doesn’t guarantee that you’ll spend exactly a quarter of that time in deep sleep. Plus, there’s no one-size-fits-all number of total sleep hours that works for everyone. These are rough guidelines, and individual sleep needs can vary. Some people may naturally have more or less deep sleep, and factors like genetics, lifestyle, and sleep disorders can influence how much deep sleep you need too.

How Can You Tell How Much Deep Sleep You’re Getting?

So, how do you know if your time spent in bed is comparable to the guidelines? It’s hard to nail down specifics, but wearable smartwatches, bracelets, or headbands can give you a rough estimation by collecting and analyzing your snooze stats.

That said, to get exact data about your Zzzs, you need to do a medical sleep study, according to Johns Hopkins Medicine. These studies monitor brain waves to analyze your sleep throughout the night.

How to Get More Deep Sleep

Hoping to spend more time in that coveted slow-wave sleep stage? Consider these tips: 

Beyond these tips, it’s always a good idea to prioritize your general sleep hygiene, which involves optimizing your sleep habits and environment in order to get the best night’s rest possible. That includes keeping a consistent sleep schedule, following a soothing bedtime routine, avoiding screens an hour before bedtime, and keeping your room dark, quiet, and cool.

What Happens If You Don’t Get Enough Deep Sleep?

Even if you get the recommended total hours of sleep each night, too little time spent in the deep sleep stage can leave you feeling groggy, drained, and tired. That’s why your body needs plenty of slow-wave sleep. Unfortunately, it’s also the stage we naturally spend less time in as we age, which explains why so many of us describe ourselves as “light sleepers.”

Over time, insufficient deep sleep is thought to have negative effects on the glymphatic system, which is a kind of maintenance system that helps clear your brain of proteins and toxins such as tau and amyloid (which are implicated in some neurodegenerative conditions), Dr. Williams explains. “Poor or disordered sleep during the middle-age years has been associated with increased risk of dementia as you age,” he adds. 

More generally, “the unintended consequences of sleep deprivation can be devastating,” Blanco says. “Physically, [those who are] sleep-deprived experience fatigue, low energy, and lack of alertness.” 

When it comes to your mental state, Blanco says a lack of sleep can affect your overall mood, which can lead to being easily agitated, upset, or depressed. “Both contributing factors negatively affect your overall health, and when you combine lack of energy and depression, it equals unsatisfactory health outcomes,” he adds. 

“Sleep deprivation, even one night, is known to have negative effects on cognitive function and physical function and performance,” Dr. Williams adds. That’s why it’s so important to make sleep a priority.

The Takeaway

While getting seven to nine hours of sleep is a good general guideline for most adults, the number of sleep cycles you experience and the time spent in each stage, including deep sleep, can vary widely. That’s why focusing on overall sleep quality and making sure you get enough total sleep to feel rested and alert during the day is key. If you find you’re more tired or fatigued than normal, or you’re experiencing sleep disturbances despite getting what you believe to be an adequate amount of sleep, it may be worth consulting a healthcare professional or sleep specialist to evaluate your snooze patterns and address any potential sleep disorders.