Based on 90-minute sleep cycles — wake up feeling refreshed, not groggy.
Sleep happens in 90-minute cycles. Each cycle includes light sleep, deep sleep, and REM sleep. Waking up at the end of a cycle means you wake naturally — feeling alert and rested. Waking mid-cycle causes that groggy feeling. We also add 14 minutes for the average time to fall asleep.
The Sleep Calculator helps you find the best time to go to bed or set your alarm, based on 90-minute sleep cycles. Whether you need to wake up for work, school, or travel — enter your target time and we show you the ideal bedtimes or wake-up times to feel your best.