Sleep Calculator
Calculate the best times to sleep and wake up based on 90-minute sleep cycles. Wake up refreshed, not groggy.
Recommended Sleep by Age
Teens (14-17)8-10 hrs
Adults (18-64)7-9 hrs
Older Adults (65+)7-8 hrs
Go to bed at:
9:45 PM
9 hours of sleep
6 cycles
Optimal
11:15 PM
7.5 hours of sleep
5 cycles
Good
12:45 AM
6 hours of sleep
4 cycles
Okay
2:15 AM
4.5 hours of sleep
3 cycles
Minimum
Frequently Asked Questions
What is a sleep cycle?+
A sleep cycle lasts about 90 minutes and moves through light sleep, deep sleep, and REM sleep. Waking between cycles (not during deep sleep) helps you feel more refreshed. Most adults need 5-6 complete cycles (7.5-9 hours).
Why do I feel groggy even after 8 hours?+
You likely woke during a deep sleep phase. Try adjusting your alarm by 15-30 minutes. The goal is to complete full 90-minute cycles, so 7.5 hours (5 cycles) may feel better than 8 hours.
How long does it take to fall asleep?+
The average person takes about 10-20 minutes to fall asleep. This calculator uses 15 minutes. If you fall asleep faster or slower, adjust your bedtime accordingly.