Bedtime calculator
Know when the alarm goes off? Enter it and count backward in whole 90-minute cycles to find a bedtime that lands you at the end of one, not the middle.
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Set the alarm, then let the room go dark.
Room for Stars fades sound and screen on its own timer, so you're not the one keeping watch. iPhone, iPad, Apple TV.
How the calculator works
The tool counts back from your wake-up time in whole 90-minute cycles, then subtracts a fall-asleep buffer to land on a bedtime. It's arithmetic, not a diagnosis: cycle length varies between people and across the night.
Why count back in 90-minute cycles
An alarm that lands you mid-cycle wakes you out of deeper sleep than one timed to the end of a cycle. The Institute of Medicine's report on sleep physiology puts the first NREM-REM cycle of the night at 70 to 100 minutes, with later cycles running longer, roughly 90 to 120 minutes (Sleep Disorders and Sleep Deprivation, National Academies Press, 2006) - which is why this counts back in whole cycles instead of just subtracting eight hours. For the fuller technical breakdown of why 90 minutes is an average and not a fixed number, see the sleep cycle calculator.