How the sleep calculator works
Sleep runs in cycles of roughly 90 minutes, moving through light sleep, deep sleep and REM sleep. Waking at the end of a cycle, when sleep is lightest, usually feels easier than being pulled out of deep sleep. The calculator counts back (or forward) in 90-minute steps and adds the time it typically takes to fall asleep – about 15 minutes for most people.
Example: to wake at 7:00 AM after five cycles (7.5 hours), go to bed around 11:15 PM: 7:00 AM − 7 h 30 min − 15 min.
How much sleep do you need?
Health organisations generally recommend 7–9 hours a night for adults, 8–10 hours for teenagers and more for children. Cycle length varies from person to person (about 80–120 minutes), so treat the results as a guide and adjust the “minutes to fall asleep” setting to match you. This tool is for general information only and is not medical advice.
Tips for better sleep
- Keep the same bedtime and wake-up time every day, including weekends.
- Avoid caffeine in the afternoon and bright screens in the last hour before bed.
- Keep your bedroom cool, dark and quiet.
- Get daylight in the morning to anchor your body clock.
Working night shifts? Total your hours with the hours calculator.
Frequently asked questions
What time should I go to bed to wake up at 6 AM?
For five full cycles go to bed around 10:15 PM; for six cycles (9 hours) around 8:45 PM; for four cycles around 11:45 PM (all including 15 minutes to fall asleep).
Is 6 hours of sleep enough?
Six hours is four full cycles and may leave you feeling rested short-term, but most adults need 7–9 hours regularly for good health.
How long is a sleep cycle?
On average about 90 minutes, although it can range from roughly 80 to 120 minutes and changes through the night.