Sleep Calculator
Best bedtimes and wake times by sleep cycle.
Reviewed by the Calculation Machine team · How we check our maths
Your values
ⓘ Live results
Results
- 6 cycles (9 hrs)
- Sleep at 21:15
- 5 cycles (7.5 hrs)
- Sleep at 22:45
- 4 cycles (6 hrs)
- Sleep at 00:15
- Recommended for adults
- 5–6 cycles, 7.5–9 hours
- Falling-asleep buffer
- 15 minutes
Quick answer
Sleep runs in roughly 90-minute cycles, so waking at a multiple of 90 minutes after falling asleep feels far less groggy.
Worked example
Worked example
Using the values the calculator loads with.
Inputs
- Wake-up time06:30 HH:MM
- Minutes to fall asleep15
Result
- 6 cycles (9 hrs)Sleep at 21:15
- 5 cycles (7.5 hrs)Sleep at 22:45
- 4 cycles (6 hrs)Sleep at 00:15
- Recommended for adults5–6 cycles, 7.5–9 hours
- Falling-asleep buffer15 minutes
How to use the Sleep Calculator
- 1Enter the time you must wake up.
- 2Set how long you usually take to fall asleep.
- 3Pick one of the suggested bedtimes.
Frequently asked questions
Why 90 minutes?
A full cycle through light, deep and REM sleep averages 90 minutes. Waking mid-deep-sleep causes grogginess.
Is 6 hours enough?
For most adults no — four cycles is a minimum for a short night, but 7–9 hours is the healthy range.
About this calculator
- Built and reviewed by the Calculation Machine team · How we build and test calculators
- Report an error