Guide
How sleep cycles work
You don't sleep in one flat block. Through the night your brain loops through stages: light sleep, deep sleep, and REM sleep, when most vivid dreaming happens. One loop is a sleep cycle, and for most adults it lasts about 90 minutes.
Why wake at the end of a cycle?
Being woken from deep sleep causes sleep inertia, the heavy, foggy feeling that can last for half an hour. Waking near the end of a cycle, in lighter sleep, usually feels easier. That is the idea behind this calculator.
How we calculate
We start at your wake time and subtract whole cycles (4, 5 or 6) plus the time you need to fall asleep, which is about 15 minutes for most people. The result is the time to be falling asleep, so get into bed a little before it.
How much do you need?
Five or six cycles (7.5–9 hours) suit most adults. Children need more, with shorter cycles. Try our kids bedtime calculator.
An honest caveat
The 90-minute figure is an average. Cycle length varies between people and through the night, and total sleep and consistent timing matter at least as much as exact cycle timing. Use the calculator as a starting point and tune the cycle length in the settings.