Find the ideal times to go to sleep or wake up based on 90-minute sleep cycles. Wake up feeling refreshed instead of groggy.
Sleep happens in 90-minute cycles, each consisting of light sleep, deep sleep, and REM (dream) sleep. If you wake up in the middle of a cycle — especially during deep sleep — you'll feel groggy and disoriented, even after 8 hours of sleep.
The key is to wake up at the end of a complete cycle, when you're in the lightest stage of sleep. This calculator shows you the ideal wake-up times based on complete 90-minute cycles, starting 14 minutes after you go to bed (the average time to fall asleep).
Best number of cycles: Most adults feel best with 5-6 cycles (7.5–9 hours). 4 cycles (6 hours) is the minimum for normal function.