Sleep Cycle Calculator

Sleep runs in cycles of about 90 minutes. Waking at the end of a cycle, when sleep is lighter, may help you feel less groggy. To wake at 7:00 AM after 5 full cycles, aim to be in bed by 11:15 PM. This calculator finds bedtimes or wake-up times for 4, 5 and 6 cycles.

Pick a mode: find a bedtime from the time you need to wake up, or find wake-up times from when you plan to go to bed. Enter the time in 24-hour format, such as 07:00 or 23:30. The tool adds about 15 minutes to fall asleep, then counts in 90-minute steps. It shows 6 cycles (9 hours), 5 cycles (7.5 hours) and 4 cycles (6 hours), and the 5-cycle option is highlighted.

Each cycle moves through light sleep, deep sleep and REM sleep, the stage when most vivid dreams happen. Early in the night, cycles hold more deep sleep. Later on, REM periods get longer. Being woken from deep sleep is what tends to cause that heavy, foggy feeling. The 90-minute figure is an average, not a fixed timer. Real cycles vary from person to person and through the night, and falling asleep can take more or less than 15 minutes. Treat the times as a guide and adjust by 15 minutes or so to see what suits you.

Total sleep still matters most. Health bodies such as the CDC advise adults to get at least 7 hours a night, which means 5 or more cycles for most people. If you often feel tired despite enough sleep, snore loudly or struggle to fall asleep, talk to a doctor. To keep other habits on track, try the Water Intake Calculator.