Sleep Calculators

How to Calculate Your Ideal Bedtime From a Required Wake-Up Time

Working backward from a fixed wake-up time, bedtime options are found by subtracting whole 90-minute sleep cycles plus the time it takes to fall asleep — the exact reverse of calculating a wake-up time from a bedtime, giving four candidate bedtimes to choose from instead of one.

How to Calculate Your Wake-Up Time From a Bedtime

Working forward from a bedtime, wake-up time options are found by adding the time it takes to fall asleep, then adding whole 90-minute sleep cycles — giving four candidate wake times spaced 90 minutes apart, each landing at a natural break between cycles rather than mid-cycle.

Understanding 90-Minute Sleep Cycles (Why 8 Hours Isn't a Magic Number)

Sleep progresses through repeating cycles of roughly 90 minutes each, and waking up between complete cycles tends to feel noticeably better than waking mid-cycle — which is why sleep calculators suggest times built around whole numbers of 90-minute cycles rather than a single fixed "8 hours" target.