Sleep Calculator
Find the best bedtimes or wake-up times based on 90-minute sleep cycles.
Try falling asleep at one of these times:
- 9:45 PM(previous day)6 cycles9 h sleep
- 11:15 PM(previous day)5 cycles7 h 30 m sleep
- 12:45 AM4 cycles6 h sleep
- 2:15 AM3 cycles4 h 30 m sleep
Each sleep cycle lasts about 90 minutes. Waking at the end of a cycle helps you feel more rested.
About the Sleep Calculator
The Sleep Calculator suggests bedtimes and wake-up times that line up with complete 90-minute sleep cycles. Waking at the end of a cycle, rather than in the middle of deep sleep, tends to leave you feeling more refreshed.
Enter the time you need to wake up and the tool works backwards to show bedtimes for six, five, four and three full cycles. Switch to the other mode and it shows wake-up times for someone falling asleep now.
A short buffer of about 14 minutes to fall asleep is built into every suggestion. All calculations are simple time arithmetic that runs entirely in the browser.
Key features
- Bedtime suggestions for a target wake-up time
- Wake-up suggestions for sleeping right now
- Based on complete 90-minute sleep cycles
- Includes time needed to fall asleep
How to use
- 1Choose whether you have a wake-up time or want to sleep now.
- 2Enter the wake-up time if needed.
- 3Pick one of the suggested times that gives you the most complete cycles.
Examples
Wake-up time 07:00Bedtimes such as 21:46 or 23:16Times are counted back in 90-minute cycles plus a short fall-asleep buffer.
Frequently asked questions
- Why 90-minute cycles?
- A typical sleep cycle lasts around 90 minutes. Waking at the end of a cycle usually feels easier than waking mid-cycle during deep sleep.
- How many cycles should I aim for?
- Most adults do well with five or six complete cycles, which is roughly seven and a half to nine hours of sleep.
- Is the fall-asleep time included?
- Yes. Each suggestion adds a short buffer of about 14 minutes to account for the time it takes to drift off.