Deep sleep makes up about 25% of your total sleep time, and it’s the stage where your body does its most critical repair work. If your sleep tracker is showing low deep sleep numbers, or you’re waking up feeling unrestored despite logging enough hours, there are concrete changes you can make to increase the time you spend in this stage.
What Deep Sleep Actually Does
Deep sleep is the third stage of non-REM sleep, characterized by slow, high-voltage brain waves called delta waves. Your brain cycles between lighter sleep stages before progressively deepening into this phase, typically within the first half of the night. During deep sleep, your heart rate drops, your breathing slows, and your muscles fully relax. This is when tissue growth and repair ramp up, your immune system strengthens, and your brain consolidates certain types of memory.
For most adults, deep sleep accounts for roughly 25% of total sleep. On a seven-hour night, that’s about 1 hour and 45 minutes. This percentage naturally declines with age, so a 60-year-old will typically get less deep sleep than a 25-year-old even if both sleep the same number of hours.
Cool Your Bedroom Down
Your body needs to drop its core temperature by about one to two degrees to initiate and maintain deep sleep. A warm room works against this process. Most sleep physicians recommend setting your thermostat between 65 and 68°F (15.6 to 20°C), with 65°F being the most commonly cited ideal. If you tend to sleep hot, err toward the lower end. If you share a bed with someone who runs cold, layering blankets on their side while keeping the room cool is a better strategy than raising the temperature for both of you.
A warm bath or shower 1 to 2 hours before bed can amplify this cooling effect. Water temperature between 104 and 108°F (40 to 42.5°C) for as little as 10 minutes draws blood to the surface of your skin, particularly your hands and feet. When you step out, that blood rapidly releases heat, causing your core temperature to drop faster than it would on its own. A meta-analysis of the existing research found this simple habit significantly shortened the time it took people to fall asleep.
Manage Light Exposure Carefully
Light is the strongest signal your brain uses to set its internal clock, and the wrong light at the wrong time directly suppresses melatonin, the hormone that initiates your slide into sleep. Blue light from phones, tablets, and laptops is particularly disruptive. In a Harvard experiment, 6.5 hours of blue light exposure suppressed melatonin for about twice as long as green light of the same brightness and shifted circadian timing by 3 hours compared to 1.5 hours for green light.
The practical takeaway: stop looking at bright screens 2 to 3 hours before bed. If that’s not realistic, use your device’s night mode or wear blue-light-blocking glasses during the last hour or two. Equally important is getting bright light exposure during the day, especially in the morning. This strengthens your circadian rhythm so your body knows when to produce melatonin later that evening.
Rethink Alcohol Before Bed
A nightcap might help you fall asleep faster, but it disrupts sleep architecture in ways that specifically hurt deep sleep. Research shows that reductions in the time it takes to reach deep sleep only occur at high doses (roughly five or more standard drinks), and even then the second half of the night becomes fragmented as your body metabolizes the alcohol. At moderate doses, you’re more likely to wake up during the night and spend less time in restorative sleep stages overall. If you drink, finishing your last drink at least 3 to 4 hours before bed gives your body time to process most of the alcohol before sleep begins.
Use Exercise Strategically
Regular physical activity is one of the most reliable ways to improve sleep quality, though the relationship with deep sleep specifically is more nuanced than you might expect. Some research shows that exercise increases lighter sleep stages rather than deep sleep directly. Still, consistent aerobic exercise improves total sleep time, reduces the time it takes to fall asleep, and decreases nighttime awakenings, all of which give your brain more opportunity to cycle into deep sleep naturally.
Timing matters less than consistency. The old advice to avoid exercise within a few hours of bedtime has largely been walked back. Moderate exercise in the evening doesn’t appear to hurt sleep for most people, though high-intensity training right before bed can raise your core temperature and heart rate enough to delay sleep onset. If you notice that late workouts leave you wired, shift them earlier. Otherwise, the best time to exercise is whenever you’ll actually do it.
Try Pink Noise
Pink noise is a type of ambient sound similar to white noise but with more emphasis on lower frequencies. Think steady rainfall or a distant waterfall. Research from Northwestern University found that short pulses of pink noise timed to match the brain’s slow waves during deep sleep increased slow-wave activity by 20% or more in some participants. Those participants also performed better on memory tests the next morning, recalling about two additional words compared to nights without the sound.
The study used a specialized system that monitored brain activity in real time and delivered sounds only during slow-wave sleep. Consumer apps that play continuous pink noise throughout the night aren’t doing the same thing, but many people still find steady low-frequency sound helpful for staying asleep. It’s low-risk and worth experimenting with.
Consider Magnesium
Magnesium plays a role in activating the part of your nervous system responsible for calming you down and preparing for sleep. Many adults don’t get enough through diet alone. A Mayo Clinic sleep specialist recommends 250 to 500 milligrams taken in a single dose at bedtime. Magnesium glycinate is gentle on the stomach and well-absorbed. Magnesium oxide is a cheaper option, though it’s more likely to cause loose stools.
Skip the magnesium sprays and lotions. Absorption through the skin is low and inefficient compared to oral supplements. If you’re already getting adequate magnesium from your diet (dark leafy greens, nuts, seeds, and whole grains are rich sources), supplementing may not add much benefit.
Keep a Consistent Sleep Schedule
Your brain distributes deep sleep unevenly across the night, front-loading most of it into the first few sleep cycles. This means the timing of when you fall asleep matters. Going to bed and waking up at the same time every day, including weekends, strengthens your circadian rhythm so your brain can reliably enter deep sleep during those early cycles. Shifting your bedtime by even an hour or two on weekends can disrupt this pattern for days.
If you’re only getting six hours of sleep, increasing your total sleep time is the single most effective way to get more deep sleep. No supplement or environmental tweak can compensate for simply not spending enough time asleep.
How Accurate Is Your Sleep Tracker?
If you’re monitoring deep sleep with a wearable, take the numbers with a grain of salt. A study comparing three popular consumer devices to clinical-grade sleep monitoring found that all of them struggled with deep sleep accuracy. The Oura Ring correctly identified deep sleep about 79.5% of the time, Fitbit caught it 61.7% of the time, and the Apple Watch only 50.5% of the time. The Apple Watch underestimated deep sleep by an average of 43 minutes per night, while Fitbit underestimated it by 15 minutes.
Overall agreement between any of these devices and clinical measurement was poor for deep sleep, with reliability scores (called intraclass correlation coefficients) ranging from just 0.13 to 0.36 out of a possible 1.0. Your tracker is useful for spotting trends over weeks and months. A single night’s deep sleep reading is not reliable enough to base decisions on. If you feel rested and alert during the day, your deep sleep is likely adequate regardless of what your wrist says.