Sleep tool
Sleep Calculator
Find the best time to go to bed or wake up in full 90-minute sleep cycles, or work out how long you slept. For adults, who need 7 or more hours. Free.
Nothing you enter leaves your device.
Inputs
Results
Enter values to see your results.
Simple steps
How it works
- 01
Choose whether you want a bedtime, a wake-up time or how long you slept.
- 02
Enter the time, and how long you usually take to fall asleep.
- 03
Select Calculate to see the times that give 4, 5 or 6 full sleep cycles.
Good to know
Frequently asked questions
Why plan around 90-minute cycles?
Sleep runs in cycles of roughly 90 minutes. Waking at the end of a cycle, rather than in deep sleep, usually feels easier.
How much sleep do adults need?
Seven hours or more a night, according to the American Academy of Sleep Medicine and the Sleep Research Society. Five or six cycles (7.5 or 9 hours) fit this best.
Why add the time to fall asleep?
Most people take 10 to 20 minutes to fall asleep. Adding it makes the suggested times more realistic; change it to suit you.
Are cycles always 90 minutes?
No. They vary from about 70 to 120 minutes between people and through the night, so the times are a guide.
Can it tell me how long I slept?
Yes. Choose to know how long you slept and enter your bedtime and wake-up time, even across midnight.
When should I see a doctor?
If you often feel tired after enough sleep, snore loudly, or have trouble sleeping for weeks.
Is anything I enter stored or sent?
No. The calculation runs in your browser. Nothing you type is saved or sent to a server.
How it is calculated
Bedtimes = wake-up time − (cycles × 90 minutes) − time to fall asleep; wake-up times = bedtime + time to fall asleep + cycles × 90 minutes, for 6, 5 and 4 cycles. Adults are recommended 7 or more hours of sleep a night (Watson and colleagues, 2015).
Sources
Last reviewed: October 14, 2026