Sleep calculator
Waking at the end of a sleep cycle, rather than in the middle of one, can help you feel less groggy.
Questions people ask
How long is a sleep cycle?
Around 90 minutes on average, though it varies from about 70 to 120 minutes between people and through the night. Treat the times here as a guide and adjust the cycle length if you know yours.
How much sleep do adults need?
The American Academy of Sleep Medicine and Sleep Research Society recommend at least 7 hours a night for adults, which is five or six cycles. Teenagers need 8–10 hours.