Sleep Cycle Calculator
Wake up refreshed by timing your sleep in full 90-minute cycles. Pick your alarm time to get ideal bedtimes — or your bedtime to get ideal wake-up times.
Enter your time
Includes ~15 minutes to fall asleep.
Go to bed at one of these times
Waking at the end of a cycle avoids deep-sleep grogginess.
How it works
Sleep comes in cycles of roughly 90 minutes, moving from light sleep to deep sleep to REM. Each cycle here is one 90-minute block, and we add about 15 minutes for the average time it takes to fall asleep:
or, in the other direction:
We show 6, 5, and 4 cycles — about 9, 7.5, and 6 hours of sleep. Six cycles is ideal for most adults; five is a reasonable minimum.
Frequently asked questions
Why 90 minutes?
A full sleep cycle — light sleep, deep sleep, and REM — lasts roughly 90 minutes in most adults. Waking up at the end of a cycle, rather than in the middle of deep sleep, is what makes you feel more refreshed.
How many sleep cycles do I need?
Most adults need 7 to 9 hours of sleep, which is about 5 to 6 full 90-minute cycles. Five cycles (7.5 hours) is a solid minimum target for most people.
What is the 15-minute buffer for?
Most people take around 15 minutes to fall asleep after getting into bed. The calculator adds this buffer so the 90-minute cycles are counted from when you actually fall asleep, not from when your head hits the pillow.
Is waking mid-cycle really that bad?
Being woken during deep sleep commonly causes grogginess, known as sleep inertia, which can last tens of minutes. Timing your alarm to the end of a cycle does not replace getting enough total sleep, but it can make waking up noticeably easier.