Sleep Calculator
Find good bedtimes for your wake-up time, using 90-minute sleep cycles.
Runs in your browser — nothing is sent or saved.
How to use the sleep calculator
- Choose "wake at" or "go to bed at".
- Type the time.
- Read the suggested times, one per sleep cycle.
- Pick the one that gives you enough rest.
How it works
Sleep runs in cycles of about 90 minutes, moving from light sleep to deep sleep and back. Waking at the end of a cycle feels easier than waking in the middle of one. This bedtime calculator counts back from your wake-up time in whole sleep cycles, and adds about 15 minutes for the time it takes to fall asleep, to suggest times to go to bed. Switch it around and it suggests wake times from a bedtime instead.
How much sleep each option gives
The suggestions cover four, five, and six cycles. Most adults do best on five or six.
| Sleep cycles | Time asleep |
|---|---|
| 4 | 6 hours |
| 5 | 7.5 hours |
| 6 | 9 hours |
A guide, not a rule
Cycle length varies from person to person and night to night, so treat the times as a helpful guess rather than an exact science. The bigger wins for good sleep are a steady schedule, a dark cool room, and easing off screens before bed.
FAQ
What time should I go to bed?
Choose "wake at", type your wake-up time, and the sleep calculator lists bedtimes that end on a full sleep cycle. It answers what time to sleep so you get five or six cycles.
What is a sleep cycle?
A sleep cycle is about 90 minutes of moving through light and deep sleep. Most people go through four to six cycles a night.
Why add 15 minutes?
Most people take around 15 minutes to fall asleep, so the tool adds that to the bedtime so the cycles start from when you are actually asleep.
Can it work out a wake up time?
Yes. Switch to "go to bed at", type your bedtime, and it lists good wake times, one per cycle.
Are my times private?
Yes. Everything runs in your browser and nothing is saved.