How much, and when
Most adults need seven to nine hours, and the people who brag about five are mostly running a deficit. The body keeps time with two systems: a clock set mainly by light, and a pressure to sleep that builds every hour you are awake. Both work best on a schedule. Pick a wake time you can hold seven days a week, within about an hour, and let bedtime follow from it.
The daytime half of the job
Get outside light within an hour of waking, even under cloud, because morning light is what anchors the clock. Caffeine lingers far longer than it seems to: half of an afternoon cup is still in your system five or six hours later, so set a cutoff around early afternoon. Alcohol is the other trap. It puts you under quickly and then breaks up the second half of the night, which is why three drinks produce eight hours in bed and the feeling of five. Keep naps under thirty minutes and before midafternoon.
The room and the last hour
Keep the bedroom cool, in the mid-sixties if you can manage it, and dark and quiet. Dim the lights and put the phone down for the last half hour, less because of the screen's color than because whatever is on it keeps your mind running. Use the bed for sleep and sex and nothing else, so that lying down becomes a cue.
When you cannot sleep
Lying there trying harder does not work. If you have been awake for what feels like twenty minutes, get up, sit somewhere dim with a dull book, and go back when you are drowsy. Turn the clock to face the wall. One bad night needs no repair: get up at the usual time and skip the long nap, and the next night tends to fix itself. Over-the-counter sleep aids are for the occasional rough patch. Follow the label, and do not make them a habit.
When to see a doctor
Trouble falling or staying asleep at least three nights a week for three months is chronic insomnia. The first-line treatment is a structured form of therapy called CBT-I, which outperforms pills over the long run. Loud snoring, gasping awake, or heavy sleepiness after a full night suggests sleep apnea, which is common, treatable, and hard on the heart when it is ignored.
Tip If you must shift your schedule, move it fifteen to thirty minutes a day. The clock adjusts gradually and resents being yanked.
