Last updated: October 2026
Deep sleep, also called slow-wave sleep or N3, is the most restorative stage of sleep. Most adults get somewhere between about 45 minutes and 2 hours a night, mostly in the first few hours, and less as they get older. The best ways to get more are enough total sleep, a regular schedule, no late caffeine and little alcohol.
Below: the sleep stages explained, how much deep sleep you need, what your tracker’s number means, deep sleep vs REM and “core” sleep, eight ways to get more, what doesn’t work, and when to see a GP.
What is deep sleep?
Deep sleep is the deepest stage of non-REM sleep, known to sleep scientists as N3. It is called slow-wave sleep after the slow, strong brain waves it produces.
In deep sleep you are hardest to wake. If something does wake you, Cleveland Clinic says the grogginess (“sleep inertia”) can last about 30 minutes. The NHS says sleepwalking happens when you partly wake from deep sleep, usually early in the night (see sleepwalking).
Two things drive it: “sleep pressure”, which builds the longer you are awake, and your body clock. That is why deep sleep is front-loaded. Your body fits in as much as it can early on, and later cycles hold more REM and lighter sleep.
The sleep stages explained: N1, N2, N3 and REM
Sleep has two main types, non-REM and REM (rapid eye movement), and non-REM has three stages. You move through them all in cycles of roughly 90 minutes, about 4 to 6 times a night.
| Stage | What happens | Share of the night (adults) | What it’s for |
|---|---|---|---|
| N1 (light) | Drifting off; lasts a few minutes | About 5% | The bridge between waking and sleep |
| N2 (light) | Brain waves slow, with bursts called sleep spindles | About 45 to 50%, the biggest share | Thought to help organise memories |
| N3 (deep) | Slow, strong brain waves; very hard to wake | Roughly 10 to 25%, falling with age | Physical repair, immune support and memory |
| REM | Brain activity close to waking; most dreaming | About 20 to 25% | Dreaming; REM periods lengthen towards morning |
Figures vary. Cleveland Clinic gives about 25% for deep sleep in adults, but in Apple’s sleep study, with lab recordings scored by trained technologists, adults averaging their late 40s spent about 12 to 13% of their sleep in deep sleep. That group included some people with sleep apnoea, which shows how much deep sleep varies with age and health.
To time your alarm around these cycles, try our sleep calculator.
How much deep sleep do you need?
There’s no official target for deep sleep. NHS advice is about total sleep: most adults need 7 to 9 hours, and if you get that, deep sleep usually takes care of itself. As a rough guide, 10 to 25% of a 7 to 9 hour night is about 40 minutes to just over 2 hours.
Age makes the biggest difference. A meta-analysis pooling 65 studies of 3,577 healthy people aged 5 to 102 found:
- Children and teenagers get the most deep sleep, and their share falls as they grow. Cleveland Clinic says children and babies need more. (Our products are for adults only.)
- Through adulthood, deep sleep, REM and total sleep time all decrease with age, while lighter sleep and time awake in the night increase.
Because these were healthy people, some decline is a normal part of ageing. The best test is how you feel: if you wake reasonably refreshed and get through the day without struggling to stay awake, you are very likely getting enough.
What your tracker’s deep sleep number means
Sleep stages are defined by brain waves, which a watch or ring can’t measure. Wearables estimate them from movement, heart rate and the time of night.
- A US study tested seven consumer trackers against lab recordings in 34 young adults. Most were good at telling sleep from wake, but sleep stage results were mixed, and they did worse on disrupted nights.
- In Apple’s validation, the most common mistake was labelling true deep sleep as core sleep, so a watch can under-count deep sleep.
A drop from 70 minutes to 50 one night is within the margin of error. A trend over weeks, say after you cut evening drinks, means more. If the scores are starting to worry you, read do sleep trackers work?
Deep sleep vs REM vs light sleep (and Apple’s “core” sleep)
| Light sleep (N1 and N2) | Deep sleep (N3) | REM sleep | |
|---|---|---|---|
| Brain waves | Slowing, with spindles | Slow and strong | Fast, close to waking |
| Dreams? | Less common | Less common | Most dreaming |
| When in the night | All night | Mostly the first half | Mostly the second half |
| Main roles | Organising memories | Physical repair, immune support, memory | Dreaming and thinking skills |
| Apple Watch label | Core | Deep | REM |
What is core sleep?
Core is Apple’s name for stages N1 and N2 together, what other trackers call light sleep. Apple avoided the word “light” because N2 often makes up more than half the night and is a normal, important part of sleep. Lots of core sleep is not a problem.
Is deep sleep better than REM?
No. They do different jobs and you need both. Deep sleep comes early, while REM builds towards morning, so cutting your night short mainly costs you REM. A regular, full night matters more than chasing one stage.
How to get more deep sleep: 8 things that help
You can’t switch deep sleep on directly, but you can give your body the time and conditions to produce it.
| Tip | What the evidence says | Strength |
|---|---|---|
| Enough total sleep | NHS: most adults need 7 to 9 hours | Strong |
| Regular sleep and wake times | NHS advice; anchors your body clock | Strong |
| Daytime exercise | Meta-analysis: small boost to deep sleep | Moderate |
| Warm bath 1 to 2 hours before bed | Meta-analysis: fall asleep faster, better rated sleep | Moderate |
| Less alcohol | Breaks up the second half of the night and delays REM | Strong |
| No caffeine for 6 hours before bed | Caffeine typically reduces deep sleep | Strong |
| A cool bedroom | Heat increases waking and reduces deep and REM sleep | Moderate |
| Pink noise | Lab studies only, using precisely timed sound | Early |
1. Give yourself enough time asleep
Late nights and early alarms squeeze every stage, so if your deep sleep looks low, check your total sleep first. If you sleep a full night and still feel rough, see why you wake up tired.
2. Keep the same sleep and wake times
The NHS says going to bed and getting up at similar times each day helps your body know when it’s time to sleep. A fixed wake time, weekends included, does most of the work; our circadian rhythm guide has a reset plan.
3. Exercise, but not right before bed
A review of 66 studies found a single bout of exercise gave small improvements in deep sleep, total sleep and how quickly people fell asleep, and regular exercise improved sleep quality. The NHS suggests being active in the day but not within 4 hours of bedtime.
4. A warm bath or shower 1 to 2 hours before bed
A 2019 review of 17 studies linked a 40 to 42.5°C bath or shower with better rated sleep, and found that one taken 1 to 2 hours before bed, even for 10 minutes, helped people fall asleep faster. Warming up sends blood to your hands and feet, which helps your core temperature fall. The review didn’t report a clear effect on deep sleep itself. Wondering about bath salts? See Epsom salt baths.
5. Cut back on alcohol, especially in the evening
A review of all known studies in healthy volunteers found alcohol helps people drop off and actually increases deep sleep in the first half of the night. The catch: it delays REM, reduces it at moderate and higher doses, and makes the second half of the night more broken. The NHS suggests avoiding alcohol in the hours before bed.
6. Stop caffeine 6 hours before bed
A systematic review found caffeine typically reduces deep sleep and increases light sleep and waking, and older adults may be more sensitive. In a US study, a strong dose taken 6 hours before bed still disrupted sleep compared with a placebo. The NHS advises no tea or coffee for at least 6 hours before bed.
7. Keep your bedroom cool
A review of temperature and sleep research found that in real life, with bedding and nightwear, a hot room increases waking and reduces both deep sleep and REM. The NHS suggests keeping your bedroom cool.
8. Pink noise (promising, but early)
In German and US lab studies, short bursts of sound (pink noise in the US study) timed exactly to a sleeper’s own slow brain waves strengthened those waves and improved overnight memory. But sound at the wrong moment did nothing, and in the US study of older adults, slow-wave activity over the whole night didn’t change. A pink noise track left playing all night is not the same thing; see brown vs white vs pink noise.
To turn these into an evening plan, see our bedtime routine for adults.
What doesn’t have good evidence
Wearable brands and social media are full of deep sleep hacks. Few are proven to change deep sleep.
- Mouth taping. We found no good trials showing it increases deep sleep, and it isn’t safe for everyone. See mouth taping.
- “Deep sleep” pillow sprays. A pleasant bedtime ritual has value, but we found no good evidence a spray increases measured deep sleep.
- Deep sleep music and meditations. These can help you relax and drift off, but the deep sleep research used precisely timed sound in a lab, not a playlist.
- Red light and gadget stacks. The basics above have far better evidence for far less money.
Supplements and deep sleep: what to know
To be straight with you: no supplement is proven to increase deep sleep, so be wary of any that promises it. A supplement can be part of a calm evening routine, but it won’t replace enough sleep and a regular schedule.
Magnesium. Magnesium contributes to the normal functioning of the nervous system and to the reduction of tiredness and fatigue. The sleep trials are small and mostly measure how quickly people fall asleep, not deep sleep; see magnesium for sleep.
Glycine. The human research on this amino acid and sleep comes down to a few small trials. In rats, glycine lowered core body temperature, part of how the body normally winds down. Whether that means more deep sleep in people isn’t proven; see glycine for sleep.
Our Magnesium Glycinate Sleep Complex is a caffeine-free berry drink combining magnesium bisglycinate and citrate with glycine, L-theanine, chamomile, passionflower, hops and oat straw, and many people make it part of their wind-down.
CBD. Our Sleep CBD Oil combines broad spectrum CBD with passion flower and a myrcene-led terpene blend. CBD isn’t a treatment for sleep problems, and there’s no good evidence it increases deep sleep. Our guide to CBD for sleep covers what the research shows.
The FSA’s 10mg a day figure is precautionary advice rather than a legal limit, set while longer-term safety research continues. At Evopure we think it is a very cautious figure, and many adults use more. If you go above it, increase slowly, and check with your GP or pharmacist first if you take any medication.
Our products are for adults only. We don’t recommend our products during pregnancy or breastfeeding.
Signs you’re short on deep sleep, and when to see a GP
You can’t feel deep sleep directly. Cleveland Clinic notes that without enough of it you can feel drained even after a long sleep. Signs your sleep isn’t refreshing you include:
- Waking up drained, even after a long night
- Feeling very tired during the day
- Finding it hard to concentrate
- Mood swings, or a headache when you wake up
Broken sleep is often the real cause, and one common reason is sleep apnoea, where breathing stops and starts during sleep.
See a GP if:
- You snore loudly, make gasping, snorting or choking noises, or your breathing stops and starts in your sleep. These are NHS-listed signs of sleep apnoea. If sleep apnoea with excessive sleepiness is confirmed, the NHS says you must not drive until symptoms like feeling very tired are under control, and you may need to tell the DVLA.
- You always feel very tired during the day.
- You’ve had trouble sleeping for several months, changing your habits hasn’t helped, or poor sleep makes it hard to cope. Our insomnia guide explains what a GP can offer, including CBT for insomnia.
Related guides
- What alcohol does to deep and REM sleep.
- Partial wakings from deep sleep can cause night terrors in children and adults.
- How to calm anxiety at night.
- Lucid dreaming and why it happens in REM sleep.
- REM sleep: how much you need and how to get more.
- The best temperature for sleep.
- Outside noise cuts deep sleep, and a 2026 lab study found earplugs blocked most of that effect: see earplugs for sleeping.
FAQs
How many hours of deep sleep is normal?
For most adults, somewhere between about 45 minutes and 2 hours a night, or roughly 10 to 25% of total sleep. Children and teenagers get more, and it falls with age.
Is deep sleep better than REM sleep?
No. Deep sleep supports physical repair, immune function and memory, while REM is when most dreaming happens. You need both, and a regular full night of 7 to 9 hours gives you enough of each.
What is core sleep on Apple Watch?
Core is Apple’s label for light sleep, stages N1 and N2. It is normally the biggest part of the night, often more than half, so a lot of core sleep is nothing to worry about.
How can I get more deep sleep naturally?
Get enough total sleep, keep regular sleep and wake times, exercise during the day, have a warm bath 1 to 2 hours before bed, avoid caffeine for 6 hours before bed, drink less alcohol and keep your bedroom cool.
Do you dream in deep sleep?
Most dreaming happens in REM sleep, not deep sleep. Deep sleep is when you are hardest to wake, and if you are woken from it you may feel groggy for up to about half an hour.
Does magnesium increase deep sleep?
It isn’t proven to. Magnesium contributes to the normal functioning of the nervous system, but the small sleep trials mostly measured how fast people fell asleep, not deep sleep.
Sources
- Patel AK et al (2024). Physiology, sleep stages. StatPearls.
- Cleveland Clinic. Sleep basics.
- Ohayon MM et al (2004). Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals. Sleep.
- Borbély AA et al (2016). The two-process model of sleep regulation: a reappraisal. Journal of Sleep Research.
- Chinoy ED et al (2021). Performance of seven consumer sleep-tracking devices compared with polysomnography. Sleep.
- Apple (2025). Estimating sleep stages from Apple Watch.
- Kredlow MA et al (2015). The effects of physical activity on sleep: a meta-analytic review. Journal of Behavioral Medicine.
- Haghayegh S et al (2019). Before-bedtime passive body heating by warm shower or bath to improve sleep. Sleep Medicine Reviews.
- Ebrahim IO et al (2013). Alcohol and sleep I: effects on normal sleep. Alcoholism: Clinical and Experimental Research.
- Clark I, Landolt HP (2017). Coffee, caffeine, and sleep: a systematic review. Sleep Medicine Reviews.
- Drake C et al (2013). Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine.
- Okamoto-Mizuno K, Mizuno K (2012). Effects of thermal environment on sleep and circadian rhythm. Journal of Physiological Anthropology.
- Ngo HV et al (2013). Auditory closed-loop stimulation of the sleep slow oscillation enhances memory. Neuron.
- Papalambros NA et al (2017). Acoustic enhancement of sleep slow oscillations and concomitant memory improvement in older adults. Frontiers in Human Neuroscience.
- Kawai N et al (2015). The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus. Neuropsychopharmacology.
- NHS. Insomnia.
- NHS Every Mind Matters. How to fall asleep faster and sleep better.
- NHS. Sleep apnoea.
- NHS. Sleepwalking.
This guide is general information, not medical advice. Evopure makes the Magnesium Glycinate Sleep Complex and Sleep CBD Oil.
