Sleep calculator
Pick the time you need to get up and see when to go to bed, or pick a bedtime and see when to set your alarm. The times line up with the end of a sleep cycle.
- Free, no sign-up
- Bedtimes and wake-up times
- 90-minute cycles
- Made in your browser
Just having a nap? Use the nap calculator
The times are worked out in cycles of about 90 minutes, plus the time it takes you to drop off. Cycle length varies from person to person, so treat them as a starting point.
To wake up at 07:00, go to bed at:
- 21:456 cycles · 9 h asleep7½ to 9 hours
- 23:155 cycles · 7 h 30 min asleep7½ to 9 hours
- 00:454 cycles · 6 h asleep
- 02:153 cycles · 4 h 30 min asleep
Most adults are advised to get around 7 to 9 hours of sleep, which is 5 or 6 cycles.
How the sleep calculator works
Sleep comes in cycles. In each one you move from light sleep into deep sleep and then into dream (REM) sleep, before surfacing towards lighter sleep again. A cycle lasts about 90 minutes on average, and a full night is usually four to six of them.
The calculator counts back from your wake-up time, or forward from your bedtime, in 90-minute steps. It adds the time it takes to fall asleep, which is 15 minutes unless you change it.
Why wake up at the end of a cycle?
Being woken from deep sleep often leaves people groggy for a while. Waking near the end of a cycle, when sleep is lighter, can feel easier. That’s why a slightly shorter night that ends at the right moment sometimes feels better than a longer one that doesn’t.
Getting the most from it
- Aim for 5 or 6 cycles. That’s 7½ to 9 hours, in line with the amount most adults are advised to get.
- Adjust to suit you. Cycle lengths differ. If you still wake up groggy, try moving your bedtime by 15 minutes either way.
- Keep it regular. Going to bed and getting up at about the same time each day, weekends included, is widely recommended.
- Put the alarm out of reach. If you tend to switch it off and roll over, put your phone or alarm across the room so you have to get up.
More ideas in our guides to how to stop hitting snooze and waking up if you sleep through alarms.
This calculator is a general guide to timing, not medical advice. If you’re regularly tired or struggle to sleep, talk to a GP or doctor.
Frequently asked questions
How long is a sleep cycle?
About 90 minutes on average, which is what this calculator uses. In practice cycles run from roughly 70 to 120 minutes, and they vary between people and through the night.
How many sleep cycles do I need?
Most adults are advised to get around 7 to 9 hours of sleep a night, which is 5 or 6 cycles of 90 minutes. Needs vary from person to person.
Why do I sometimes wake up groggy?
Being woken during deep sleep often leaves people feeling groggy for a while. The idea behind timing your alarm to the end of a cycle is to wake from lighter sleep instead.
Why does it add time to fall asleep?
Cycles only start once you’re asleep, not when you get into bed. Most people take somewhere around 10 to 20 minutes to drop off, so the calculator adds 15 minutes unless you change it.
How accurate is it?
It’s a rule of thumb, not a measurement of your own sleep. Use the times as a starting point and adjust by 15 minutes or so until waking up feels easier.
Is this medical advice?
No. It’s a general guide to timing only. If you’re regularly tired, struggle to sleep or snore heavily, talk to a GP or doctor.