Most adults spend 10% to 20% of the night in deep sleep, roughly 40 to 110 minutes out of a full seven to nine hours. If your sleep tracker is showing you numbers on the low end, or you’re waking up feeling unrested despite enough total sleep, there are several evidence-backed ways to push that number higher. The key levers are body temperature, light exposure, exercise timing, alcohol habits, and your sleep environment.
Cool Your Room to 60–67°F
Your body needs to drop its core temperature to enter and stay in deep sleep. Thermoregulation is directly tied to how much time you spend in slow-wave sleep, the restorative stage where tissue repair, immune function, and memory consolidation happen. The Cleveland Clinic recommends keeping your bedroom between 60 and 67°F (15 to 19°C). Think of your bedroom as a cave: cool, dark, and quiet.
If air conditioning isn’t an option, a fan, breathable bedding, or cooling mattress pad can help. The goal is to avoid anything that forces your body to work at regulating its temperature overnight, because that effort pulls you out of deep sleep stages.
Take a Warm Shower 1–2 Hours Before Bed
This sounds counterintuitive given the cooling advice, but it works because of what happens after the shower. Warm water (around 104–109°F) brings blood to the surface of your skin. Once you step out, that heat dissipates rapidly, causing a sharp drop in core body temperature that signals your brain it’s time for sleep. A meta-analysis of existing research found that a warm shower or bath taken one to two hours before bedtime, for as little as 10 minutes, significantly shortened the time it took to fall asleep and improved overall sleep quality.
Exercise Earlier in the Day
Regular physical activity is one of the most reliable ways to increase deep sleep. A review published in Sports Medicine found that evening exercise actually helped people fall asleep faster and spend more time in deep sleep, with one important caveat: high-intensity workouts like interval training done less than an hour before bed had the opposite effect, making it harder to fall asleep and reducing sleep quality.
A safe rule of thumb is to finish any vigorous exercise at least two hours before you plan to get into bed. Moderate activity like walking or yoga closer to bedtime is generally fine. If you’re choosing between morning and afternoon workouts specifically for sleep benefits, both work. Consistency matters more than timing.
Block Blue Light After Sunset
Your brain produces melatonin in response to darkness, and melatonin helps regulate the timing of your sleep stages, including when deep sleep kicks in. Blue light, the wavelength emitted most strongly by phone screens, tablets, and LED bulbs, is particularly effective at suppressing that process. In a Harvard experiment, 6.5 hours of blue light exposure suppressed melatonin for twice as long as green light of equal brightness and shifted the body’s internal clock by three hours compared to 1.5 hours for green light.
You don’t need to avoid screens entirely. Dimming your phone, using a warm-toned night mode, or wearing blue-light-blocking glasses in the two to three hours before bed all reduce the impact. Swapping bright overhead lights for lamps with warm bulbs makes a meaningful difference too.
Cut Alcohol, Especially Regular Use
Alcohol is one of the most common deep sleep disruptors, and its effects are worse than most people realize. While a drink may help you fall asleep faster, it fragments sleep architecture throughout the night, pulling you out of slow-wave sleep and into lighter stages. The damage compounds with regular use. Research from the American Academy of Sleep Medicine found that long-term heavy drinkers had significantly less deep sleep than non-drinkers, with men averaging just 6.6% slow-wave sleep compared to 12% in controls. That reduction persisted even after more than 700 days of sobriety, suggesting that chronic alcohol use causes lasting changes to sleep regulation.
Even moderate drinking affects deep sleep. If you’re trying to maximize it, the simplest move is to stop drinking at least three to four hours before bed, or skip it on nights when sleep quality matters most.
Try Pink Noise
Pink noise is similar to white noise but deeper and more balanced, like steady rainfall or wind through trees. Research at Northwestern University found that precisely timed pulses of pink noise, delivered during slow-wave sleep, enhanced deep sleep activity in participants. Those who showed a 20% or greater increase in slow-wave brain activity recalled about two more words on a memory test the next morning, a meaningful boost.
The study used a system that monitored brain waves in real time and played sound only during slow-wave periods, stopping if the person woke up. Consumer apps and devices that approximate this approach are available, though they’re less precise than lab equipment. Even a simple pink noise machine running through the night can help mask disruptions that would otherwise pull you out of deep sleep.
Consider Magnesium
Magnesium plays a role in balancing the neurotransmitters that help your brain shift between alertness and relaxation. It also supports melatonin production. Many people don’t get enough through diet alone, and supplementing can help if you’re deficient. Mayo Clinic recommends 250 to 500 milligrams taken as a single dose at bedtime. Magnesium glycinate is the form most commonly suggested for sleep, as it’s easier on the stomach than other types.
This isn’t a dramatic fix for most people, but if your magnesium levels are low (common in older adults and people who eat processed diets), correcting the deficiency can noticeably improve sleep depth.
Know What’s Normal for Your Age
Children and teenagers get the most deep sleep. From there, deep sleep declines gradually throughout adulthood and levels off around your 70s. If you’re 50 and your tracker shows less deep sleep than it did a decade ago, that’s expected. Adults typically land somewhere between 40 and 110 minutes per night, and anything in that range is normal.
The decline isn’t entirely inevitable, though. People who stay physically active, maintain a healthy weight, and follow consistent sleep schedules tend to preserve more deep sleep than those who don’t. The strategies above won’t reverse aging, but they can keep you closer to the higher end of the normal range for your age rather than the lower end. Small, consistent changes to your sleep environment and habits tend to matter more than any single supplement or gadget.