Sleep Calculator
Calculate optimal bedtimes and wake times based on sleep cycles. Wake up feeling refreshed by timing your sleep to complete full 90-minute cycles.
This calculator assumes it takes about 15 minutes to fall asleep and uses 90-minute sleep cycles.
Enter a time to calculate optimal sleep schedules.
How It Works
Sleep happens in cycles of approximately 90 minutes. Each cycle includes light sleep, deep sleep, and REM sleep. Waking up at the end of a complete cycle—during light sleep— leaves you feeling more refreshed than waking in the middle of deep sleep.
This calculator factors in about 15 minutes to fall asleep, then calculates times that align with completing 3, 4, 5, or 6 full sleep cycles. Most adults need 5-6 cycles (7.5-9 hours) for optimal rest.
Individual sleep cycles can vary from 80-110 minutes, and falling asleep time varies too. Use these times as a starting point and adjust based on how you feel when waking.
Frequently Asked Questions
How much sleep do I actually need?
Adults typically need 7-9 hours (5-6 cycles). Teenagers need 8-10 hours, and children need even more. Sleep needs are individual—some people function well on 7 hours, others need 9. Chronic sleep deprivation affects health significantly.
Why do I feel groggy even after 8 hours?
You may be waking during deep sleep. Try adjusting your wake time by 15-30 minutes in either direction. Also consider sleep quality factors: room temperature, light, noise, alcohol consumption, and screen time before bed.
Is it bad to sleep too long?
Regularly sleeping more than 9-10 hours is associated with health issues, though it's unclear if oversleeping causes problems or results from them. Occasional long sleep to recover from sleep debt is normal. Consistent oversleeping warrants a doctor visit.
Should I wake up at the same time every day?
Yes, consistency helps regulate your circadian rhythm. Waking at the same time daily—even on weekends—is more important than going to bed at the same time. Your body will naturally get sleepy at the right time once wake time is consistent.
What about naps?
Power naps of 20-30 minutes can boost alertness without entering deep sleep. A full 90-minute nap completes one cycle and can be refreshing. Avoid napping after 3 PM as it can interfere with nighttime sleep.