Sleep cycle calculator
When should you go to bed?
Sleep runs in roughly 90-minute cycles. Wake at the end of one and you feel rested; wake in the middle and you feel groggy. Pick the right time below.
If you fall asleep right now… We'll find your best wake-up times.
How it works
How long is one sleep cycle?
A full cycle averages about 90 minutes and moves through light sleep, deep sleep and REM. Most people complete 4–6 cycles a night, which is why this tool counts in whole cycles rather than fixed hours.
Why do I wake up groggy even after 8 hours?
If your alarm goes off in the middle of deep sleep, you get "sleep inertia" — that heavy, foggy feeling. Waking at the end of a cycle, in light sleep, usually feels far easier even with slightly less total sleep.
What does the fall-asleep slider do?
Most people take around 15 minutes to actually fall asleep. Drag the slider to match how long it takes you, and the calculator shifts every suggested time to match your real sleep, not just lights-out.