Sleep cycle calculator
Pick a wake time or a bed time and we will work backward (or forward) in 90-minute blocks, with a 14-minute fall-asleep buffer baked in. Five to six full cycles is the sweet spot for most adults.
Calculator assumes 90-minute sleep cycles and a 14-minute fall-asleep buffer. 5 to 6 full cycles is the sweet spot for most adults.
Try going to bed in 14 minutes.
Lights out at 04:32. The earliest 5-cycle wake-up lands at 12:16.
One 90-minute cycle
Light → Deep → REM
23:46
5 full sleep cycles
7h 30m asleep
22:16
6 full sleep cycles
9h asleep
01:16
4 full sleep cycles
6h asleep
02:46
3 full sleep cycles
4h 30m asleep
20:46
7 full sleep cycles
10h 30m asleep
Informational. For sleep disorders, see a clinician.
"Eight hours" is a population average that hides the thing that actually makes you feel rested: where in a sleep cycle the alarm catches you. Sleep moves in roughly 90-minute cycles, light to deep to REM and back. If your alarm fires in the middle of deep sleep, you wake up heavy, slow, and confused for the first half hour, even after a full eight hours. If it fires at the end of a cycle, you can wake up clear-headed on six. The calculator above just does that arithmetic for you. It is not a substitute for actually sleeping enough, and the cycle length varies a bit from person to person, but on most nights aiming for a multiple of 90 minutes is a measurable upgrade over a round number chosen for psychological convenience.
A cycle is roughly fifty minutes of progressively deeper non-REM, then around twenty minutes of REM where most dreaming happens, then a brief surfacing toward light sleep before the next cycle starts. The first few cycles of the night are deep-sleep heavy. The cycles in the second half tilt toward REM. Waking near the end of any cycle is the target; waking in the deep block of an early cycle is the worst case. The 14-minute fall-asleep buffer the calculator adds is the population median for healthy sleepers with normal sleep hygiene. If you usually take half an hour to fall asleep, add 15 minutes to the bedtime; if you drop off in five, subtract 10.
Hitting cycle boundaries is a tactic, not a strategy. The strategy is consistent total sleep time, a regular schedule, dim light in the hour before bed, and a cool, dark room. If you have been running on five hours all week, going to bed at a "cycle boundary" tonight will not undo the deficit; only several nights of longer sleep will. For early starts the night before a flight or exam, treat the calculator as a hedge: line up the alarm with a cycle end so the wake-up is as gentle as possible. If you want to track focus blocks instead of sleep, the Pomodoro timer is purpose-built for that. For a single morning alarm with snooze, use the alarm clock.