How it works
Sleep runs in cycles of about 90 minutes. Waking at the end of a cycle usually feels easier than waking from deep sleep. The calculator counts back (or forward) in 90-minute steps and adds the time it takes to fall asleep, 15 minutes by default.
Most adults need 7 to 9 hours, so 5 or 6 cycles is the sweet spot.
Worked example
To wake at 7:00 AM: 6 cycles (9 h) + 15 min means bed at 9:45 PM. 5 cycles (7.5 h) means 11:15 PM. 4 cycles (6 h) means 12:45 AM.
Frequently asked questions
What time should I go to bed to wake up at 7?
9:45 PM or 11:15 PM, for 6 or 5 full cycles if it takes about 15 minutes to fall asleep.
How long is a sleep cycle?
About 90 minutes on average, though it ranges from roughly 70 to 120.
How much sleep do adults need?
The CDC recommends at least 7 hours a night for adults 18 to 60.
Is this medical advice?
No. For ongoing sleep trouble, talk to a doctor.