Sleep Calculator
Bedtimes and wake times aligned to 90-minute sleep cycles.
How it works
Sleep runs in cycles of roughly 90 minutes, moving from light sleep to deep sleep and into REM. Waking at the end of a cycle, in light sleep, feels far better than waking mid-cycle even if the total is longer.
Most adults need five to six cycles, which is seven and a half to nine hours. The 90-minute figure is an average — individual cycles run from about 70 to 120 minutes — so treat these as targets rather than alarms to set your life by.