Sleep calculator
Find the best time to go to bed or wake up based on 90-minute sleep cycles, so you wake up refreshed instead of in the middle of deep sleep.
- Free
- No sign-up
- No file uploaded
- Windows, Mac, Android, iPhone
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About this tool
Sleep comes in cycles of about 90 minutes. Waking at the end of a cycle rather than in the middle feels easier. Enter your wake-up time or bedtime, and the calculator suggests the best times.
When to use it
Before an exam or an early flight
Need to get up at 5 a.m.? Choose the bedtime that ends on a full cycle.
Building a routine
Regular bed and wake times improve sleep quality: find the pair that works for you.
A nap or a short night
If the night has to be short, 4 full cycles (6 h) beat waking in the middle of a cycle.
How to use
- Choose your question.
- Enter your wake-up time or bedtime.
- Pick one of the suggested times.
How it works
The calculation adds the time to fall asleep (14 minutes on average, adjustable) and then multiples of 90 minutes. For a 7:00 wake-up it suggests 21:46 (6 cycles), 23:16 (5 cycles), 00:46 or 02:16.
Real cycle length varies from 80 to 110 minutes between people and through the night: treat these times as guides. Nothing is sent, the calculation runs on your device.
Tips for best results
- Adults need 7 to 9 hours of sleep: aim for 5 or 6 cycles.
- Set the time to fall asleep from experience: it is longer after screens or coffee.
- Keep the same schedule at weekends to avoid “social jet lag”.
- Avoid screens in the hour before bed.
Common problems and fixes
I still wake up tired
Cycle length varies: adjust the time to fall asleep by a few minutes, and check your total sleep time.
The suggested times are too late
Choose fewer cycles, but a night under 6 hours should not become a habit.
The “now” time is wrong
It follows your device clock, refreshed every 30 seconds.
Frequently asked questions
How long is a sleep cycle?
About 90 minutes on average for adults, 80 to 110 minutes depending on the person.
How many cycles do I need per night?
5 to 6 cycles, or 7.5 to 9 hours, suit most adults.
Why wake up at the end of a cycle?
Sleep is light at the end of a cycle: waking up is easier than from deep sleep.
Is this calculator medical advice?
No. For persistent sleep problems, see a doctor.
Related searches
Still stuck?
Ask on the forum: the category, the tool, your device sheet and the test result will be filled in for you.