Sleep-Cycle Calculator
Wake up refreshed, not groggy — find the best bedtimes (or wake times) around full 90-minute cycles.
Why this works: you sleep in ~90-minute cycles. Waking at the end of a cycle feels refreshed; waking mid-cycle feels groggy — even with more total sleep.
Go to bed at one of these times:
9:46 PMideal
6 cycles · 9.0 h sleep
11:16 PMideal
5 cycles · 7.5 h sleep
12:46 AM
4 cycles · 6.0 h sleep
2:16 AM
3 cycles · 4.5 h sleep
Assumes ~14 minutes to fall asleep and 90-minute cycles (these vary person to person). Most adults do best on 5–6 full cycles (7.5–9 hours). Consistency of wake time matters more than hitting an exact number.