Sleep Calculator
Calculate the best time to go to bed or wake up based on 90-minute sleep cycles. Optimize your rest and wake up feeling refreshed.
Why Sleep Cycles Matter
A good night's sleep consists of 5-6 complete sleep cycles. Each cycle lasts about 90 minutes and moves through stages: light sleep, deep sleep, and REM (Rapid Eye Movement) sleep.
Waking up in the middle of a deep sleep stage leaves you feeling groggy and tired (sleep inertia). Waking up at the end of a cycle, when you are in a lighter sleep stage, makes you feel refreshed and alert.
How this calculator works
This tool calculates wake-up times (or bedtimes) by counting backwards or forwards in 90-minute increments. It also adds an average of 15 minutes for the time it takes most people to fall asleep.
- 7.5 Hours: 5 complete cycles (Recommended average).
- 9 Hours: 6 complete cycles (Great for athletes/teens).
- 6 Hours: 4 complete cycles (Minimum for decent function).
- 4.5 Hours: 3 complete cycles (Emergency short sleep).
This ensures you wake up at the optimal moment in your sleep rhythm.
? Frequently Asked Questions
The calculator assumes an average of 14-15 minutes to fall asleep. If you know you take longer (e.g., 30 mins), try to get into bed 15 minutes earlier than the suggested time.
90 minutes is the average. Cycles typically range from 80 to 110 minutes depending on the person and the time of night. However, aiming for 90-minute intervals is a solid strategy for most people.
Naps should also follow sleep cycles to avoid grogginess. A 20-minute power nap keeps you in light sleep. A 90-minute nap completes a full cycle.