Sleep Calculator
Best bedtime or wake-up time by sleep cycles.
One sleep cycle lasts about 90 minutes. Waking at the end of a cycle usually feels easier than waking in the middle of deep sleep. Most adults need 5 or 6 cycles (7.5 to 9 hours).
About this tool
Sleep Calculator suggests bedtimes for a wake-up time, or alarm times for a bedtime, so you wake at the end of a sleep cycle. It assumes cycles of about 90 minutes and adds the time you usually need to fall asleep.
How to use Sleep Calculator
- Choose "Wake up at" or "Go to bed at".
- Enter the time and how long you take to fall asleep.
- Pick one of the suggested times.
Questions people ask
How does the calculator work?
Bedtime = wake-up time − (cycles × 90 minutes) − time to fall asleep. For a 7:00 wake-up with 15 minutes to fall asleep, 6 cycles gives 9:45 pm and 5 cycles gives 11:15 pm.
How much sleep do adults need?
Health bodies such as the US National Sleep Foundation recommend 7 to 9 hours for adults aged 18 to 64, and 7 to 8 hours over 65. That is 5 or 6 full cycles. Teenagers need 8 to 10 hours.
Is every sleep cycle exactly 90 minutes?
No. Cycles range from about 70 to 120 minutes and change through the night. 90 minutes is an average, so use the results as a starting point and shift by 10 to 15 minutes if you still wake up groggy.