Work out bedtime by sleep cycles instantly with clear inputs, formula shown and shareable results.
Sleep runs in cycles of roughly 90 minutes, and waking at the end of a cycle — in light sleep rather than deep sleep — feels far better than waking mid-cycle. Counting back whole cycles from the alarm, plus time to fall asleep, gives the bedtime to aim for.
Cycle-based bedtime
bedtime = wake time - (cycles x cycle length) - sleep latency
It averages 90 but ranges from 70 to 120 minutes and lengthens through the night. Treat it as an approximation rather than a clock.
Five cycles is 7.5 hours, within the recommended range for most adults. Four cycles at six hours is a workable minimum but not sustainable long term.