Most healthy adults get about 15 to 20% of their sleep as deep sleep, which works out to roughly 1 to 1.5 hours on a 7.5-hour night. There's no official daily target for deep sleep the way there is for total sleep. The most reliable way to get enough is to sleep enough hours, because deep sleep is a share of the night, not a separate goal.
This page turns that share into minutes for your own night, shows how it changes with age, and explains why the number on your tracker may be off.
Free toolSleep Needs by AgeRecommended hours for every age, from newborns to over-65s.Deep sleep calculator: how to work out your number
Deep sleep minutes = hours asleep x 60 x deep sleep share. Use about 20% if you're under 30, and about 15% if you're over 60 (the medians from the lab study below).
Worked example: you sleep 7.5 hours and you're 28. That's 7.5 x 60 = 450 minutes, and 450 x 0.20 = 90 minutes of deep sleep.
| Hours asleep | At 13% | At 15% | At 20% | At 25% |
|---|---|---|---|---|
| 6 h | 47 min | 54 min | 72 min | 90 min |
| 6.5 h | 51 min | 59 min | 78 min | 98 min |
| 7 h | 55 min | 63 min | 84 min | 105 min |
| 7.5 h | 59 min | 68 min | 90 min | 113 min |
| 8 h | 62 min | 72 min | 96 min | 120 min |
| 9 h | 70 min | 81 min | 108 min | 135 min |
Read across the row for your usual sleep. The 13% and 25% columns show how much the number can vary; healthy people in the lab study fell both below and above them. The table makes the main point clearer than any rule: someone sleeping 6 hours at 20% gets less deep sleep than someone sleeping 8 hours at 15%. Total sleep moves the number more than anything else. Not sure how much you're really getting? The hours of sleep calculator works it out from your bedtime and alarm.
What is a normal amount of deep sleep?
In lab studies of healthy adults, deep sleep is usually somewhere around 15 to 21% of total sleep. In a polysomnography study of 100 carefully screened healthy sleepers, the median share of deep (N3) sleep was 20.7% in adults aged 30 and under and 14.9% in adults over 60.
Applied to their median sleep times, that's roughly 85 minutes of deep sleep a night for the younger group and about 55 minutes for the older group. Those are middle values, not minimums. The ranges in that study were wide, and plenty of healthy people sat well above or below the median.
So a fair answer to "how much deep sleep do I need" is: about an hour to an hour and a half for most adults, a bit less as you get older, as long as you feel rested.
Deep sleep by age
Children and teens get the most deep sleep, and the share falls gradually through adulthood. A large meta-analysis of 65 studies covering ages 5 to 102 found that the percentage of deep (slow-wave) sleep goes down with age, both in children and adolescents and in adults.
| Age group | Typical deep sleep share | On a typical night |
|---|---|---|
| Children and teens | Highest of any age | Depends on total sleep, which is also longer |
| Adults 30 and under | About 21% (median) | Around 85 minutes |
| Adults over 60 | About 15% (median) | Around 55 minutes |
The adult figures come from the 100-sleeper study above. The child row is left without a number on purpose: the meta-analysis confirms the trend, but its summary doesn't give one figure for each age, and we won't make one up.
A lower share after 60 is normal, not a sign that something is wrong. Total sleep needs shift too; the sleep needs by age calculator shows the recommended hours for every age group.
Is 1 hour of deep sleep enough?
For most adults, about an hour of deep sleep a night is within the normal range, especially over 40. If you feel rested and alert during the day, an hour is very likely fine.
What matters more is the pattern over weeks, not one night. A single low night after a late bedtime, a drink or a stressful day is expected. If you're sleeping 7 hours or more, feel refreshed, and your tracker still says 40 minutes, the tracker is a likely suspect.
Can you trust your tracker's deep sleep number?
Not to the minute. Consumer devices are fairly good at telling sleep from wake, but much weaker at sorting sleep into stages.
When researchers tested seven consumer sleep trackers against lab polysomnography, most devices detected sleep well, but their sleep stage results were inconsistent, and they tended to do worse on nights of disrupted sleep. A wristband or ring estimates stages from movement and heart rate. A lab scores them from brain waves.
Use your tracker's deep sleep number as a rough trend over weeks, not a nightly grade. If it rises when you sleep longer, that's useful. If it swings 30 minutes from one night to the next with nothing changing, that's mostly noise. The same caution applies to sleep cycle alarm apps.
Does sleeping longer give you more deep sleep?
Yes, in the sense that matters for the calculator. Deep sleep is a share of the night, so more total sleep generally means more minutes of it, and most of it comes in the first two or three cycles. A steady bedtime protects those early cycles; plan one with the sleep calculator. Regular exercise has a small beneficial effect on deep sleep in a meta-analysis of 66 studies. Alcohol can raise deep sleep early in the night while disrupting the second half, so a higher tracker number after a drink isn't a better night. Late caffeine can cut into sleep too; the caffeine calculator shows what's left at bedtime.
If you sleep a full night and still wake up exhausted, snore loudly, or someone has noticed you stop breathing in your sleep, talk to a doctor. Those point to problems that a sleep study can check properly, and no tracker can rule them out.