Sleep
When should you go to bed to wake up rested?
Work back from the time you have to be up. The calculator lands you on whole sleep cycles and adds the minutes most people take to drift off.
Cycles run roughly 90 minutes but vary by person and shorten toward morning, so treat these as starting points. Adults are advised seven hours or more; the six-cycle time is the one to aim at.
Why cycles, not just hours
Sleep runs in cycles of roughly ninety minutes, moving from light sleep through deep sleep and into REM. Waking at the end of a cycle tends to feel easier than being pulled out of deep sleep in the middle of one, which is why two people can sleep the same number of hours and feel completely different at the alarm. The times above are spaced a cycle apart for that reason. Cycles are not a metronome, though: they vary between people and get shorter as the night goes on, so treat the result as a first guess and adjust by how the mornings feel.
How much sleep to aim for
The consensus recommendation for adults is seven hours or more per night, regularly. The six-cycle bedtime is nine hours in bed and the five-cycle one is seven and a half, which is why those two are the ones to aim between. Four cycles is six hours: fine on an odd night, not a plan.
The part that matters more than the bedtime
Wake time is the anchor. A steady wake time, including weekends, does more for how rested you feel than any single early night, because it is what your internal clock keys on. This is the logic Orbit follows: you set one bedtime that describes your rhythm, the app derives the rest, and the morning line arrives at the same time every day.
Questions people ask
How many hours of sleep do adults need?
The American Academy of Sleep Medicine and the Sleep Research Society recommend seven or more hours a night for adults on a regular basis. Some people need more; very few do well on less.
Is a sleep cycle really 90 minutes?
On average, roughly. Cycles run about 70 to 120 minutes and tend to shorten toward morning, so a cycle-based bedtime is a starting point you adjust by how you feel on waking.
Why do I wake up tired after eight hours?
Common reasons are waking mid-cycle, an irregular schedule that shifts your internal clock, alcohol or late caffeine, and light or noise in the room. Keeping wake time steady for two weeks is the usual first experiment.