SleepUtility
A free sleep calculator that finds the best bedtime or wake-up time based on 90-minute sleep cycles.
SleepUtility is a free sleep calculator. You pick the time you need to wake up and it counts backwards in 90-minute sleep cycles to find a bedtime. Or you pick when you are going to bed, or tap Sleep Now, and it counts forward to the best times to set an alarm.
Each result lands at the end of a full cycle, when you are in light sleep and waking up is easiest. The calculator also adds 15 minutes, the typical time it takes to fall asleep, so the times reflect when you are actually asleep rather than when you get into bed.
No ads, no sign-up
The calculator works without an account and shows no ads. An optional free account only exists to save one personal setting: how long it usually takes you to fall asleep. That keeps the tool fast for a quick answer at night, which is when most people use it.
More than one calculator
Around the main tool sits a set of focused calculators, each answering one question:
- a nap calculator for power naps and full-cycle naps
- a sleep debt calculator for the past week
- a REM sleep calculator
- a jet lag calculator that shifts your schedule before you fly
- calculators for sleep efficiency, sleep schedules and caffeine at bedtime
- a short chronotype quiz
Short pages answer common questions such as whether five or six hours of sleep is enough, with a bedtime table for common wake-up times. The result is a small, fast site that answers the question people actually search for, instead of a sign-up wall in front of a simple calculation.