Sleep Calculator
Find the best bedtime or wake-up time.
Go to bed at one of these times
More free tools
See Sleep Calculator in action
Free Sleep Cycle Calculator
Sleep runs in cycles of about 90 minutes. Waking in the middle of a cycle leaves you groggy, while waking at the end feels natural. Tell the calculator when you need to wake up and it suggests the bedtimes that complete whole cycles.
You can also enter a bedtime, or use 'sleep now', to see the best wake-up times. The calculation allows about 15 minutes to fall asleep.
Use it in 4 steps
Choose whether you want a bedtime or wake-up time.
Enter your time.
Pick one of the suggested times.
Set your alarm.
Key features
Cycle-based
Times aligned to 90-minute cycles.
Two modes
Find bedtime or find wake-up time.
Sleep now
Best wake times if you go to bed now.
Adjustable
Change the time to fall asleep.
A real example, step by step
(each 90-minute cycle; 5–6 cycles ≈ 7.5–9 hours)
Who uses this tool
Students and shift workers
Plan bedtimes around fixed wake-up times.
Parents
Help children build regular sleep routines.
Athletes
Optimise recovery with full sleep cycles.
Tips for the best results
- Aim for 5–6 complete cycles (7.5–9 hours) if you can.
- Allow about 15 minutes to fall asleep.
- Keep wake-up times consistent, even at weekends.
- Avoid screens and caffeine before bed.
Common mistakes to avoid
- Ignoring the time it takes to fall asleep.
- Cutting sleep short to fit in an extra hour of activity.
- Changing bedtime and wake time drastically each day.
Frequently asked questions
How many hours of sleep do I need?
Most adults need 7 to 9 hours, which is 5 to 6 full sleep cycles.
What is a sleep cycle?
A repeating pattern of light, deep and REM sleep that lasts roughly 90 minutes.
Why allow 15 minutes to fall asleep?
That is the average time most people need to drift off.
Is this medical advice?
No. It is a planning aid. Talk to a doctor about sleep problems.
How long is a sleep cycle?
About 90 minutes, moving through light, deep and REM sleep.
How many hours of sleep do adults need?
Most adults need 7–9 hours a night.
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