Sleep Calculator
Work backwards from your wake-up time to bedtimes that complete full 90-minute sleep cycles.
Enter your details below.
How to use
- Enter the hour you want to wake up (0 to 23).
- Enter the minute you want to wake up (0 to 59).
- Pick one of the three bedtimes for 4, 5, or 6 sleep cycles.
About this tool
Sleep runs in roughly 90-minute cycles, and waking at the end of a cycle usually feels easier than waking mid-cycle. This tool subtracts 4, 5, or 6 cycles plus about 15 minutes to fall asleep from your chosen wake time, giving three bedtimes to pick from. The result is general information only, not medical advice, and it cannot fix poor sleep quality or a medical sleep problem.
Frequently asked questions
Why 90-minute cycles?
Sleep moves through light, deep, and dream stages in cycles averaging about 90 minutes, so whole cycles tend to end in lighter sleep.
What if none of the bedtimes suits me?
Pick the closest one and shift your wake time slightly, or aim for the nearest whole number of cycles rather than forcing an awkward bedtime.