What Is a Sleep Cycle?
During sleep, your brain moves through repeating cycles of roughly 90 minutes each. Waking up in the middle of a cycle — especially during deep sleep — can leave you feeling groggy, while waking up right at the end of a cycle usually feels more refreshing. This calculator suggests bedtimes or wake-up times based on full 90-minute cycles.
How to Use It
If you're heading to bed now, click "I'm Going to Bed Now" to see wake-up times after 3 to 6 cycles. If you need to wake up at a specific time (for work, say), enter that time below to find out when to go to sleep. Most adults are recommended 5–6 cycles (7.5–9 hours); those options are highlighted in the list.