Waking up in the middle of a sleep cycle leaves you feeling groggy, even if you slept for 8 hours. This calculator uses the science of 90-minute sleep cycles to help you find the perfect time to fall asleep or wake up. By aligning your alarm with the end of a complete cycle, you'll feel more refreshed and energized. Simply enter your desired wake-up time or bedtime, and we'll calculate the optimal times for you. The tool accounts for the average 14 minutes it takes to fall asleep, so your timing is always accurate.