Is 4 Hours of Sleep Enough?
Four hours of sleep is not enough for adults. It is three hours short of the AASM minimum of 7 hours, and because 4 hours is not a whole number of 90-minute cycles, an alarm at the 4-hour mark often wakes you mid-cycle, which makes the morning feel worse.
Bedtimes for 4 hours of sleep
Each bedtime includes 15 minutes to fall asleep.
Enough for adults?
No
Sleep cycles
2.7
Sleep debt per week vs. 7 h
21 h
| To wake up at | Go to bed at |
|---|---|
| 5:30 AM | 1:15 AM |
| 6:00 AM | 1:45 AM |
| 6:30 AM | 2:15 AM |
| 7:00 AM | 2:45 AM |
| 7:30 AM | 3:15 AM |
| 8:00 AM | 3:45 AM |
Want a different wake-up time? The sleep calculator finds bedtimes that end on a full sleep cycle.
What the research says about 4 hours of sleep
In a 2003 study by Van Dongen and colleagues, people restricted to 4 hours a night for two weeks showed steadily worsening attention and memory, while rating themselves as only slightly sleepy. If you only have about 4 hours, 4.5 hours (three full cycles) usually feels better than 4.
How much sleep you need by age
These are the National Sleep Foundation's recommended ranges.
| Age | Hours per night |
|---|---|
| School-age children (6–13) | 9–11 |
| Teenagers (14–17) | 8–10 |
| Adults (18–64) | 7–9 |
| Older adults (65+) | 7–8 |
Other sleep lengths
- Is 3 hours of sleep enough?
- Is 5 hours of sleep enough?
- Is 6 hours of sleep enough?
- Is 6.5 hours of sleep enough?
- Is 7 hours of sleep enough?
- Is 8 hours of sleep enough?
- Is 9 hours of sleep enough?
Running short most nights? The sleep debt calculator shows how much you owe and how long it takes to pay back.
More free sleep tools
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Sleep Debt Calculator
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REM Sleep Calculator
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Jet Lag Calculator
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Sleep Efficiency Calculator
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Sleep Schedule Calculator
A day-by-day plan to fix your sleep schedule or adjust to daylight saving time.
Caffeine Calculator
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Chronotype Quiz
Five questions to find out if you are a morning lark or a night owl.
Frequently asked questions
Is 4 hours of sleep enough?
Four hours of sleep is not enough for adults. It is three hours short of the AASM minimum of 7 hours, and because 4 hours is not a whole number of 90-minute cycles, an alarm at the 4-hour mark often wakes you mid-cycle, which makes the morning feel worse.
How many sleep cycles is 4 hours of sleep?
About 2.7 cycles of 90 minutes. Because that isn't a whole number, waking at 4 hours often interrupts a cycle; 3 h or 4 h 30 min usually feels better.
What time should I go to bed to get 4 hours of sleep?
Count back 4 hours and 15 minutes from your alarm. To wake at 7:00 AM, go to bed at 2:45 AM.