Sleep Cycle Calculator: Bedtime and Wake Time
Find the best time to go to bed or wake up. It counts back or forward in 90-minute sleep cycles from your wake time or bedtime, allows for the time you take to fall asleep, and checks the result against the recommended hours for your age group.
Written by Suhaib Hassan. Figures are estimates you can edit. Our methodology.
It uses a fixed 90-minute cycle. Real cycles run about 70 to 120 minutes and change through the night, so treat the times as a good starting point.
A whole number of cycles often leaves you less groggy than the same total hours cut mid-cycle. This makes that arithmetic quick.
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| Go to bed at | Cycles | Sleep |
|---|
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Sleep stages and waking up
A night is a run of cycles of about 90 minutes, each moving through light sleep, deep sleep and REM. Waking at the end of a cycle, from light sleep, usually feels better than waking from deep sleep.
| Stage | Share of a night | What happens | If you wake in it |
|---|---|---|---|
| N1 light sleep | about 5% | Drifting off, muscles relax, heart rate slows. | Easy to wake, feel alert |
| N2 core sleep | 45–55% | Body temperature falls, memory processing. | Mild grogginess |
| N3 deep sleep | 15–25% | Physical recovery, growth hormone release. Mostly early in the night. | Heaviest grogginess |
| REM sleep | 20–25% | Vivid dreams, memory and mood processing. Longer near morning. | Usually easy to wake |
Formulas
How the numbers are worked out.
Bedtime for a wake time
Count back whole cycles from the time you want to wake, then allow for falling asleep.
bedtime = wake − (cycles × 90 min) − fall-asleep timeWake time from a bedtime
Add the time to fall asleep to your bedtime, then count forward whole cycles.
wake = bedtime + fall-asleep time + (cycles × 90 min)Sleep you get
Whole cycles times 90 minutes. Time in bed is that plus the time to fall asleep.
sleep = cycles × 90 minWorked examples
Illustrative figures, each checked by hand. The first is the default setup.
Wake at 6:30 AM
5 cycles and 14 minutes to fall asleep (the default).
6:30 AM − 450 min − 14 min = 10:46 PM
4 cycles: 12:16 AM · 6 cycles: 9:16 PM
Bed at 11:00 PM
14 minutes to fall asleep.
5 cycles: 11:14 PM + 7 h 30 min = 6:44 AM
4 cycles: 5:14 AM
Nap at 2:00 PM
14 minutes to fall asleep.
20 min power nap: 2:34 PM
90 min full cycle: 3:44 PM
How to use the sleep calculator
- Choose whether you know your wake time, your bedtime, or want a nap.
- Enter the time and how long you usually take to fall asleep.
- Pick the age group so the result is compared with the recommended hours.
- Choose the option that fits your schedule. Five cycles (7.5 hours) suits most adults.
This is a planning tool, not medical advice. If you regularly sleep badly, snore heavily, or feel exhausted after a full night, speak to a doctor.
By Suhaib Hassan · Reviewed 29 September 2026 · How CalculatePilot verifies formulas →
Sources
- National Sleep Foundation, National Sleep Foundation's sleep time duration recommendations (Hirshkowitz et al., Sleep Health, 2015).
- American Academy of Sleep Medicine, Sleep stages and cycles.
- Carskadon & Dement, Normal human sleep: an overview, in Principles and Practice of Sleep Medicine.
Frequently asked questions
How long is a sleep cycle?
About 90 minutes on average, moving through light sleep, deep sleep and REM. Individual cycles vary from about 70 to 120 minutes, and the mix shifts through the night.
How many hours of sleep do I need?
The National Sleep Foundation recommends 7 to 9 hours for adults aged 18 to 64, 8 to 10 for teens, and 7 to 8 for adults 65 and over.
Why do I wake up tired after 8 hours?
Waking during deep sleep causes sleep inertia, a heavy groggy feeling that can last for a while. Shifting the time by 15 to 30 minutes can change how you feel.
What is the best length for a nap?
A 10 to 20 minute nap gives an alertness boost with little grogginess. A 90-minute nap is a full cycle. Around 30 to 60 minutes often means waking from deep sleep.
Why include time to fall asleep?
Cycles only start once you are asleep. If you take 15 minutes to drift off, you need to be in bed 15 minutes earlier to get the same amount of sleep.
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