You slept for eight hours, but your smartwatch says you only got 40 minutes of deep sleep. Should you be worried?

Not necessarily. Deep sleep plays an important role in physical recovery, memory, and feeling refreshed. But getting more of it isn't as simple as going to bed earlier. Your age, daily habits, and sleep quality all influence how much deep sleep you get.

The good news? Small changes to your routine may help. Here are eight research-backed ways to improve deep sleep, plus how much you need and what your sleep tracker might be missing.

Key Takeaways:

• Adults spend roughly 10% to 20% of their sleep in the deep sleep stage, although individual needs vary.
• Regular exercise, consistent sleep schedules, and limiting caffeine may help support deeper sleep.
• Deep sleep naturally decreases with age, so younger and older adults shouldn't expect identical numbers.
• Sleep trackers can misjudge deep sleep. How rested you feel matters more than a single night's reading.

What Is Deep Sleep, and Why Does It Matter?

Deep sleep, also called slow-wave sleep or N3 sleep, is the deepest stage of non-REM sleep. During this stage, brain waves slow down, your muscles relax, and waking up becomes more difficult.

Your body uses this time for important recovery processes, including tissue repair and growth hormone release. Deep sleep also plays a role in memory and learning.

Unlike REM sleep, which becomes more prominent later in the night, deep sleep is concentrated in the first part of your sleep period. (1)

That's one reason a full night's sleep matters. Your brain moves through several sleep stages, and each has a different job.

How Much Deep Sleep Do You Need?

Most adults spend around 10% to 20% of their total sleep time in deep sleep, although there's no single medically established target that applies to everyone. (2)

Here's what that range looks like:

These figures are reference ranges, not strict requirements.

Deep sleep also changes with age. Children spend more time in slow-wave sleep, while older adults tend to spend considerably less. (1)

For perspective, someone in their 60s may record less deep sleep than someone in their 20s without necessarily having a sleep disorder.

What matters more is getting enough total sleep and feeling rested during the day. The National Institutes of Health recommends 7–9 hours of sleep for most adults. (3)

How to Get More Deep Sleep Naturally

You can't directly control how long your brain stays in deep sleep. However, several habits may improve your sleep quality and create better conditions for restorative sleep.

1. Keep a Consistent Sleep Schedule

Going to bed and waking up around the same time helps regulate your circadian rhythm, your body's internal sleep-wake clock.

Try keeping your wake-up time consistent, even on weekends. If your schedule changes every few days, your body has a harder time predicting when it's time to sleep.

The CDC recommends maintaining a regular sleep schedule as part of healthy sleep habits. (4)

2. Exercise Regularly

Exercise is one of the more promising ways to support deeper sleep.

A 2025 meta-analysis involving 1,214 adults with sleep disorders found that exercise improved sleep efficiency, reduced nighttime wakefulness, and increased slow-wave sleep.

The researchers also reported stronger deep sleep benefits with exercise sessions at least four times per week, particularly among people with obstructive sleep apnea. (5)

You don't need an intense workout every day. Brisk walking, cycling, swimming, or moderate strength training are reasonable places to start.

Consistency matters more than exhausting yourself.

3. Avoid Caffeine Too Close to Bedtime

That afternoon coffee might be affecting your sleep more than you realize.

A 2023 meta-analysis of 24 studies found that caffeine consumption reduced total sleep time by an average of 45 minutes and deep sleep by 11.4 minutes. (6)

Timing and dosage also make a difference.

In a randomized trial published in 2024, researchers found that 400 mg of caffeine disrupted sleep when consumed within 12 hours of bedtime. A smaller 100 mg dose showed no statistically significant sleep disruption under the tested conditions. (7)

If you go to bed at 10 p.m., try moving your last coffee to the morning, particularly if you're sensitive to caffeine.

4. Limit Alcohol Before Bed

Alcohol can make you feel sleepy, but falling asleep faster doesn't mean you're getting better sleep.

Research has found that alcohol may increase slow-wave sleep during the first half of the night while disrupting sleep later on. It can also interfere with REM sleep. (8)

In other words, more deep sleep early in the night doesn't automatically mean better recovery.

Avoid relying on alcohol as a sleep aid, especially if you already wake up feeling tired.

5. Keep Your Bedroom Cool, Dark, and Quiet

Your sleeping environment can make a surprising difference.

A room that's too warm, bright, or noisy may interrupt sleep or make it harder to fall asleep in the first place.

A few simple changes can help:

• Keep your bedroom comfortably cool.
• Use blackout curtains if outdoor light enters your room.
• Reduce disruptive noise with earplugs or other suitable options.
• Keep your phone and other bright screens away from bedtime.

These changes support better sleep quality, although they aren't guaranteed to increase N3 sleep specifically. (4)

6. Get Natural Daylight During the Day

Your brain uses light as a signal to help regulate sleep timing.

Getting daylight exposure, particularly after waking up, helps reinforce your natural sleep-wake rhythm. At night, reducing bright light helps prepare your body for sleep.

Try spending some time outdoors in the morning. Even a short walk can combine daylight exposure with physical activity.

The direct effect of morning light on deep sleep duration remains less certain than its role in circadian timing.

7. Try a Warm Bath Before Bed

A warm shower or bath may help you fall asleep more comfortably.

A 2019 systematic review and meta-analysis found that bathing in warm water around 104°F–109°F (40°C–43°C) approximately 1–2 hours before bedtime improved some sleep measures, including the time needed to fall asleep. (9)

The proposed explanation involves body temperature. After leaving warm water, your body releases heat, which may help signal that it's time for sleep.

However, the research doesn't establish that warm bathing directly increases deep sleep.

8. Get Enough Total Sleep

Before trying to increase your deep sleep percentage, check your total sleep duration.

Most adults need 7–9 hours per night. Consistently sleeping for only five or six hours limits the time available for your body to complete its normal sleep cycles. (3)

And remember, deep sleep isn't the only stage that matters. REM sleep and lighter stages have important functions, too.

Rather than chasing a particular deep sleep score, prioritize enough sleep time and a schedule you can maintain.

What Causes a Lack of Deep Sleep?

Sometimes, poor deep sleep has less to do with bedtime habits and more to do with underlying factors.

Potential contributors include:

• Aging: Slow-wave sleep naturally decreases as people get older.
• Stress: Mental tension and nighttime arousal can interfere with restful sleep.
• Irregular sleep schedules: Frequent changes in bedtime can disturb your sleep-wake rhythm.
• Caffeine and alcohol: Both can alter sleep patterns, depending on dose and timing.
• Sleep disorders: Conditions such as obstructive sleep apnea can repeatedly interrupt sleep.
• Medications: Certain medications may change sleep architecture.

If you're getting enough hours but still wake up exhausted, it may be worth investigating the cause rather than trying another sleep hack.

How Can You Tell If You're Getting Enough Deep Sleep?

Your smartwatch can give you useful sleep trends, but it can't measure sleep stages with the same precision as a clinical sleep study.

A 2024 study compared five commercial sleep trackers against laboratory polysomnography in 53 young adults. Researchers found that several devices overestimated shorter periods of deep sleep and underestimated longer periods. (10)

So, a reading of 35 minutes doesn't necessarily mean you got exactly 35 minutes.

Instead, look at the bigger picture. Are you getting enough total sleep? Do you wake up feeling refreshed? Can you stay alert throughout the day?

If you experience persistent daytime sleepiness, loud snoring, gasping during sleep, or frequent nighttime awakenings, speak with a healthcare professional. A sleep study may help identify underlying problems.

Final Words

Getting more deep sleep isn't about hitting a perfect number on your smartwatch. A consistent bedtime, regular exercise, less late-day caffeine, and enough total sleep are good places to start.

Pay attention to how you feel, not just what your sleep app reports.

For additional support, consider Omre Glycine + NAC. It combines glycine and NAC, two amino acid compounds your body uses to produce glutathione, an important antioxidant.

FAQs

Is 1 hour of deep sleep enough?

One hour may be within a normal range for many adults. If you sleep for eight hours, 60 minutes represents 12.5% of your total sleep time. However, age, sleep quality, and individual differences matter.

Why am i getting only 30 minutes of deep sleep?

Age, caffeine, irregular sleep, medications, or sleep disorders may contribute. Your tracker could also be underestimating your deep sleep. Check longer-term patterns rather than relying on one night's reading.

Can you get too much deep sleep?

There's no established upper limit that automatically makes deep sleep unhealthy. A high reading on a wearable isn't enough to identify a problem. Other symptoms and your total sleep quality provide more useful context.

Does magnesium help with deep sleep?

Some research suggests magnesium may help certain aspects of sleep, particularly in people with low magnesium intake. However, strong human evidence showing that magnesium supplements reliably increase N3 deep sleep is lacking.

How long does it take to improve deep sleep?

It depends on what's affecting your sleep. Improving caffeine timing or bedroom conditions may help relatively quickly, while exercise-related changes may take several weeks. There's no guaranteed timeline for increasing deep sleep minutes.

References

1. National Heart, Lung, and Blood Institute. How Sleep Works: Sleep Phases and Stages.
2. Sleep Foundation. How Much Deep Sleep Do You Need?.
3. National Heart, Lung, and Blood Institute. How Much Sleep Is Enough?.
4. Centers for Disease Control and Prevention. About Sleep.
5. Wang P, et al. (2025). Comparative efficacy of exercise modalities on sleep architecture in adults with sleep disorders. Sleep Medicine.
6. Gardiner C, et al. (2023). The effect of caffeine on subsequent sleep: A systematic review and meta-analysis. Sleep Medicine Reviews.
7. Dose and timing effects of caffeine on subsequent sleep: A randomized clinical crossover trial. (2024).
8. Ebrahim IO, et al. (2013). Alcohol and sleep I: Effects on normal sleep. Alcoholism: Clinical and Experimental Research.
9. Haghayegh S, et al. (2019). Before-bedtime passive body heating by warm shower or bath to improve sleep: A systematic review and meta-analysis. Sleep Medicine Reviews.
10. Kainec KA, et al. (2024). Evaluating Accuracy in Five Commercial Sleep-Tracking Devices Compared to Research-Grade Actigraphy and Polysomnography. Sensors.