Sleep Calculator
Find the best time to sleep or wake up based on 90-minute sleep cycles.
100% Client-Side
Assumes ~15 min to fall asleep
Recommended Times
9:45 PM
6 cycles (9h)
Optimal
11:15 PM
5 cycles (7.5h)
Optimal
12:45 AM
4 cycles (6h)
2:15 AM
3 cycles (4.5h)
What is Sleep Calculator?
A sleep calculator determines the ideal times to fall asleep or wake up based on 90-minute sleep cycles. Waking between cycles (rather than in the middle of one) helps you feel more rested, even with fewer hours of sleep, by avoiding interrupting deep or REM sleep.
How to Use
- Enter the time you need to wake up, or the time you want to go to sleep
- The calculator shows optimal sleep and wake times based on 90-minute cycles
- Account for the average 15 minutes it takes to fall asleep
- Choose the option that gives you 5-6 complete sleep cycles (7.5-9 hours)
Frequently Asked Questions
- How many hours of sleep do I need?
- Most adults need 7-9 hours. Teenagers need 8-10, and children need even more. Quality (completing full cycles) matters as much as quantity.
- What is a sleep cycle?
- A sleep cycle lasts about 90 minutes and includes light sleep, deep sleep, and REM (dream) sleep. You go through 4-6 cycles per night, with more REM occurring in later cycles.
- Why do I feel groggy even after 8 hours of sleep?
- You likely woke up during deep sleep rather than at the end of a cycle. Try adjusting your alarm by 15-30 minutes earlier or later to catch a cycle transition.