Sleep Calculator
Calculate optimal bedtimes based on your wake-up time and 90-minute sleep cycles for better rest.
6 Cycles (9h)
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5 Cycles (7.5h) —
4 Cycles (6h) —
3 Cycles (4.5h) —
How to Use This Calculator
Enter your desired wake-up time (hour and minute in 24-hour format). The calculator suggests 4 bedtimes based on completing 3, 4, 5, or 6 full 90-minute sleep cycles, plus 15 minutes to fall asleep.
Formula
Bedtime = Wake Time - (Cycles × 90 minutes) - 15 minutes to fall asleep
6 cycles = 9h 15min | 5 cycles = 7h 45min | 4 cycles = 6h 15min | 3 cycles = 4h 45min
6 cycles = 9h 15min | 5 cycles = 7h 45min | 4 cycles = 6h 15min | 3 cycles = 4h 45min
Example
Example: Wake at 7:00 AM: Ideal bedtimes are 9:45 PM (6 cycles), 11:15 PM (5 cycles), 12:45 AM (4 cycles), or 2:15 AM (3 cycles).
Frequently Asked Questions
- A sleep cycle lasts about 90 minutes and includes light sleep, deep sleep, and REM sleep. Most adults need 4-6 complete cycles (6-9 hours) per night.
- Waking during deep sleep causes grogginess (sleep inertia). Timing your alarm to the end of a complete cycle helps you wake feeling refreshed.
- The average person takes 15 minutes to fall asleep. This calculator adds 15 minutes to the suggested bedtimes to account for this.
- Most adults need 7-9 hours. The sweet spot for most people is 5 cycles (7.5 hours) or 6 cycles (9 hours). 4 cycles (6 hours) is the minimum.