Wake Up at 4:00 AM?

How these are calculated

Each option counts back from 4:00 AM in 90-minute blocks — the average length of one full sleep cycle — plus 15 minutes to account for the time it typically takes to actually fall asleep. Waking up at the boundary between cycles, rather than in the middle of one, tends to feel less groggy even with a similar total amount of sleep.

Want to start from a different wake-up time, or work forward from right now instead? Use the full Sleep Calculator.