Sleep Cycle Calculator
Enter the time you need to wake up – or when you go to bed. The calculator adds the time it takes to fall asleep and shows times for 4, 5 and 6 sleep cycles of roughly 90 minutes. Example: to wake up at 7:00 am, go to bed at 11:15 pm for 5 cycles (7.5 hours of sleep) or at 9:45 pm for 6 cycles. This is a rule of thumb: real cycles vary in length.
Source: NINDS (NIH) – Brain Basics: Understanding Sleep (REM sleep first occurs about 90 minutes after falling asleep; several NREM/REM cycles per night). Updated: .
How it is calculated
How the sleep calculator works
During sleep, light sleep, deep sleep and REM sleep alternate in cycles. On average a cycle lasts about 90 minutes. Waking at the end of a cycle often feels less groggy than being woken from deep sleep – hence the idea of timing the alarm to whole cycles.
How to use the sleep calculator
- Under “I know”, choose when you need to wake up – or when you go to bed.
- Enter the wake-up time or bedtime, or tick “I am going to bed now”; adjust the time to fall asleep if needed.
- Read the times for 4, 5 and 6 sleep cycles and pick the one that fits.
- Wake-up time known: bedtime = wake-up time − time to fall asleep − cycles × 90 minutes
- Bedtime known: wake-up time = bedtime + time to fall asleep + cycles × 90 minutes
Worked example
Your alarm goes off at 07:00 and you need about 15 minutes to fall asleep. For 5 cycles: 5 × 90 = 450 minutes = 7 hours 30 minutes. 07:00 − 0:15 − 7:30 = 23:15 (11:15 pm). For 6 cycles (9 hours) it would be 21:45, for 4 cycles (6 hours) 00:45.
Sleep cycle chart: when to go to bed
| Wake-up time | 5 cycles (7.5 h sleep) | 6 cycles (9 h sleep) | 4 cycles (6 h sleep) |
|---|---|---|---|
| 5:00 am | 9:15 pm | 7:45 pm | 10:45 pm |
| 5:30 am | 9:45 pm | 8:15 pm | 11:15 pm |
| 6:00 am | 10:15 pm | 8:45 pm | 11:45 pm |
| 6:30 am | 10:45 pm | 9:15 pm | 12:15 am |
| 7:00 am | 11:15 pm | 9:45 pm | 12:45 am |
| 7:30 am | 11:45 pm | 10:15 pm | 1:15 am |
| 8:00 am | 12:15 am | 10:45 pm | 1:45 am |
All times include 15 minutes to fall asleep. Going the other way, bed at 10:00 pm gives wake-up times of 5:45 am (5 cycles) or 7:15 am (6 cycles); bed at 11:00 pm gives 6:45 am or 8:15 am; bed at midnight gives 7:45 am or 9:15 am.
Why only a rule of thumb?
The 90 minutes are an average. According to the standard textbook Principles and Practice of Sleep Medicine (Carskadon & Dement), the first cycle of the night lasts about 70 to 100 minutes and later cycles about 90 to 120 minutes. The US National Institute of Neurological Disorders and Stroke (NINDS) notes that REM sleep first occurs about 90 minutes after falling asleep and that REM periods get longer towards morning. The time it takes to fall asleep varies as well, so treat the times as a guide, not a precise target.
How much sleep do adults need?
The American Academy of Sleep Medicine and the Sleep Research Society recommend that adults (18 to 60 years) sleep 7 or more hours per night on a regular basis (Watson et al., 2015). The table therefore marks which options reach that amount. 4 cycles (6 hours) fall short and are at best an exception.
This calculator is not a substitute for medical advice. If you feel tired despite enough sleep, snore heavily or have trouble falling or staying asleep, have it checked by a doctor.
Related tools: set a short power nap with the online timer, see how much to drink with the water intake calculator, and estimate your energy use with the calories burned calculator.
Frequently asked questions
What time should I go to bed if I wake up at 6 am?
With 15 minutes to fall asleep: 22:15 (10:15 pm) for 5 cycles (7.5 hours of sleep), 20:45 (8:45 pm) for 6 cycles (9 hours). 4 cycles (bedtime 23:45) give only 6 hours of sleep.
How long is a sleep cycle?
About 90 minutes on average, in reality roughly 70 to 120 minutes. The first cycle is usually shorter, later ones longer, and the length differs from person to person.
How many sleep cycles do I need?
Sleep experts recommend at least 7 hours of sleep for adults. That is about 5 cycles (7.5 hours) – most people have 4 to 6 cycles per night.
Why 15 minutes to fall asleep?
It is only the calculator’s default. Many people fall asleep in about that time, some faster, some slower – enter your own value.
Will I definitely wake up refreshed if I time my sleep in cycles?
No. Because cycles vary in length, the calculation cannot hit the end of a cycle exactly. Getting enough sleep on a regular schedule matters more than the exact minute.
What time should I go to bed if I wake up at 7 am?
With 15 minutes to fall asleep: 11:15 pm for 5 cycles (7.5 hours), 9:45 pm for 6 cycles, or 12:45 am for 4 cycles.
When should I wake up if I go to bed now?
Tick “I am going to bed now” and the calculator uses the current time. Going to bed at 11 pm means falling asleep around 11:15 pm; 5 cycles end at 6:45 am, 6 cycles at 8:15 am.
Sources and legal basis
- NINDS (NIH) – Brain Basics: Understanding Sleep (REM sleep first occurs about 90 minutes after falling asleep; several NREM/REM cycles per night)
- doi:10.1016/B978-0-323-24288-2.00002-7: Carskadon MA, Dement WC: Normal Human Sleep. In: Principles and Practice of Sleep Medicine, 6th ed., Elsevier 2017, pp. 15–24 (length of the NREM–REM cycle)
- doi:10.5664/jcsm.4758: Watson NF et al.: Recommended Amount of Sleep for a Healthy Adult – Joint Consensus Statement of the AASM and SRS. J Clin Sleep Med 2015;11(6):591–592
As of: · Editorial policy
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