It's 11 PM and you need to wake up at 7 AM. You wonder: How many hours of sleep will I actually get? You also know that waking during a deep sleep phase leaves you groggy. But waking between sleep cycles feels refreshed. You want to time your sleep to wake at the right moment. You could calculate it manually. Count the hours, subtract fall-asleep time, account for sleep cycles. But you need to understand sleep cycle lengths and how they work. Or you could use a sleep calculator to instantly show that if you sleep now, you should wake up at 6:30 AM (after 5 complete sleep cycles) instead of 7:00 AM to feel more rested. A sleep calculator estimates ideal bedtimes and wake times based on sleep cycles, showing when to sleep to complete full cycle phases and wake during light sleep for maximum alertness. Sleep calculators are used by people trying to improve sleep quality, night shift workers planning rest periods, travelers dealing with jet lag, students managing study schedules, and a...