What time should I go to bed?
Sleep runs in cycles of about 90 minutes. Waking up between cycles, instead of in the middle of one, is what makes the difference between feeling rested and feeling groggy. Pick a mode below and get times built around full cycles.
Go to bed at one of these times
Times include a 15-minute buffer to fall asleep. The highlighted option gives 5–6 full cycles (7.5–9 hours), the range most adults sleep best on.
Why sleep cycles matter more than hours
A single sleep cycle moves through light sleep, deep sleep, and REM sleep, and lasts roughly 90 minutes for most adults. Waking up mid-cycle, especially during deep sleep, is what causes that heavy, disoriented feeling even after a full night in bed. Timing your bedtime or alarm to land between cycles — at the 4.5, 6, 7.5, or 9-hour mark — tends to produce a noticeably easier wake-up, even with the same total sleep.
This isn't a substitute for consistent sleep habits. A regular wake time, daylight exposure in the morning, and cutting caffeine in the afternoon all matter more over time than any single night's timing. But when you need to work backward from an alarm, or figure out how late you can push bedtime, cycle-based timing is the more reliable guide than just "aim for 8 hours."
Frequently asked questions
How many sleep cycles do I need?
Most adults need 5 to 6 full cycles a night — about 7.5 to 9 hours. Some people function on 4 cycles (6 hours) but this is closer to the minimum than the ideal.
Why do I feel groggy even after 8 hours of sleep?
You likely woke up mid-cycle rather than between cycles. Two nights of the same total sleep can feel very different depending on which sleep stage your alarm interrupted.
How long does it actually take to fall asleep?
About 15 minutes on average, which is the buffer this calculator adds automatically. If you consistently take much longer, that's usually a sign to look at caffeine timing, screen use, or a wind-down routine before bed.