Sleep Cycle Calculator
Bedtimes and wake times that land at the end of a sleep cycle rather than in the middle of one.
Sleep runs in cycles of roughly 90 minutes. Waking at the end of a cycle, in light sleep, generally feels better than being pulled out of deep sleep partway through one — which is the whole idea behind timing an alarm to a multiple of 90 minutes.
How this is worked out
A night moves through light sleep, deep slow-wave sleep and REM, and back again, four to six times. Deep sleep dominates the early cycles and REM the later ones, which is why the last couple of hours before waking are mostly dream sleep and why cutting a night short costs you REM disproportionately.
The 90-minute figure is an average, not a constant — individual cycles run anywhere from 70 to 120 minutes and get longer as the night goes on. Total sleep time matters considerably more than cycle timing: most adults need seven to nine hours, teenagers eight to ten, and no amount of clever alarm timing compensates for five.
If you are consistently sleeping enough hours and still waking unrefreshed, timing is unlikely to be the problem. Persistent insomnia, loud snoring with pauses in breathing, or daytime sleepiness that interferes with life are worth raising with a doctor.
This calculator runs entirely in your browser. Nothing you enter is transmitted to us, saved on our servers, or shared with anyone.
Common questions
How many hours of sleep do I need?
Seven to nine hours for most adults, eight to ten for teenagers, and seven or more from age 65. Individual needs vary, but the number of adults who genuinely function well on six is far smaller than the number who believe they do.
Is it better to wake after five cycles or sleep another 20 minutes?
If you are short on sleep overall, take the extra sleep. Cycle timing is a refinement worth using when you are already getting enough.