Sleep Cycle Calculator

How it works

The calculator adds a 14-minute fall-asleep buffer to whole multiples of a 90-minute sleep cycle, then walks through 3 to 6 cycles (4.5 to 9 hours) to produce a list of bed or wake times, wrapping the result around a 24-hour clock. Entering a wake-up time subtracts each cycle length to find candidate bedtimes; entering a bedtime adds each cycle length to find candidate wake-up times.

FAQ

Why does the calculator suggest multiple bedtimes or wake times instead of just one?

Because there's no single 'right' amount of sleep — it shows every option from 3 to 6 full cycles (4.5 to 9 hours) so you can pick based on how much time you actually have, rather than being told only one answer.

Where does the 14-minute number come from?

It's a commonly cited average time for a healthy adult to fall asleep after getting into bed, added on top of the sleep cycles themselves — your own time to fall asleep will vary, which is the biggest source of error in any cycle-based calculation like this.