Why wake-up time matters
Sleep moves through cycles of light, deep and REM sleep that last about 90 minutes each. Waking at the end of a cycle, when sleep is lightest, usually feels easier than being pulled out of deep sleep halfway through one, even if you slept for the same time overall.
How the times are worked out
- Each cycle is counted as 90 minutes, and the time it takes you to fall asleep is added on.
- Five or six cycles — 7½ to 9 hours — is the amount most adults need, so those times are marked as recommended.
- Three or four cycles are shown for short nights, but they are not enough sleep to rely on.
How to use the sleep calculator
- Choose what you know: the time you must wake up, the time you will go to bed, or that you are going to bed now.
- Adjust the minutes it takes you to fall asleep. Most people need 10 to 20.
- Pick a time from the list and set your alarm, or plan your bedtime.
Good to know
- Cycle length differs between people, from about 70 to 120 minutes, so treat the times as a starting point and adjust by 10–15 minutes if needed.
- A regular schedule, even on weekends, does more for sleep quality than any single night’s timing.
- If you often feel tired after a full night’s sleep, or snore loudly, speak to a doctor.
Frequently asked questions
How many hours of sleep do I need?
Adults generally need 7 to 9 hours; teenagers 8 to 10; school-age children 9 to 12.
What time should I sleep to wake up at 6 am?
Around 8:45 pm or 10:15 pm for six or five full cycles, with 15 minutes to fall asleep. Choose a different wake-up time above to see others.
Are 90-minute sleep cycles exact?
No. 90 minutes is an average; cycles get longer towards the morning. The calculator is a guide, not a precise prediction.