Sleep Cycle Calculator
Sleep runs in roughly 90-minute cycles. Timing your alarm for the end of a cycle rather than the middle of deep sleep is what separates waking up clear-headed from waking up groggy.
Go to bed at one of these times
- Well rested
9:45 PM
6 cycles · 9h of sleep
- Well rested
11:15 PM
5 cycles · 7h 30m of sleep
- Adequate
12:45 AM
4 cycles · 6h of sleep
- Short
2:15 AM
3 cycles · 4h 30m of sleep
Sleep progresses through cycles of roughly 90 minutes, and waking at the end of a cycle rather than mid-way through deep sleep tends to feel less groggy. These times allow 15 minutes to fall asleep. Cycle length genuinely varies between people and across the night, so treat the times as a guide rather than a schedule — total sleep and consistent timing matter more than landing on an exact minute.