Find the best times to wake up or go to sleep based on 90-minute sleep cycles.
Sleep occurs in approximately 90-minute cycles that progress through light sleep, deep sleep, and REM (dream) sleep. Waking up at the end of a complete cycle, rather than in the middle of deep sleep, tends to leave you feeling more alert and refreshed. Most adults need 4-6 complete cycles (6-9 hours) per night.
Enter the time you need to wake up, and the calculator counts backward in 90-minute intervals (plus your estimated time to fall asleep) to suggest optimal bedtimes. Alternatively, enter when you plan to go to sleep and it calculates the best wake-up times.
The ideal amount of sleep for most adults is 7-9 hours per night (roughly 5-6 complete cycles). Consistently getting fewer than 6 hours or more than 10 hours is associated with negative health outcomes.