Bedtime Sleep Cycle Calculator

This calculator works out the best times to go to bed so you wake up at the end of a sleep cycle feeling refreshed, based on the time you need to be up. Sleep is not uniform through the night; it runs in cycles of about ninety minutes, moving from light sleep down into deep sleep and up through REM, and how rested you feel on waking depends a lot on where in that cycle the alarm goes off. Wake at the end of a cycle, in lighter sleep, and you tend to feel clearer; wake in the middle of deep sleep and you feel groggy even after plenty of hours. The trick is to time your bedtime so that a whole number of cycles fits before your wake time, allowing for the roughly fifteen minutes it takes most people to actually fall asleep. You enter the time you need to wake, and the calculator gives you several recommended bedtimes, each corresponding to a whole number of cycles, typically six cycles for about nine hours, five for seven and a half, and four for six. Aim for the latest bedtime that still gives you five or six cycles on a normal night, or an earlier one if you can. It is a guide based on average cycle length, which varies between people, so use it alongside how you actually feel. Sweet dreams.

Allows about 15 minutes to fall asleep and uses 90-minute cycles. Cycle length varies between people, so use this as a guide alongside how you feel.