Sleep calculator

The usual recommendation for adults is 7 to 9 hours of sleep, and 7 to 8 from age 65. Count that back from your get-up time, then allow about 15 minutes to fall asleep. With a 7am alarm, aim for bed between 9:45 and 11:45pm. The calculator below works it out for any time, from either end of the night.

How much sleep do you need?

Seven to 9 hours a night is what the National Sleep Foundation's expert panel recommends for adults under 65, and 7 to 8 hours after that. The American Academy of Sleep Medicine and the Sleep Research Society, the two big US sleep societies, put it more simply for adults 18 to 60: 7 hours or more a night, on a regular basis. The panel also allowed that some people do fine on a bit more or less.

Those hours run from falling asleep to waking up. Most people wake briefly in the night, and more so with age, so the sleep you get is usually a little less than the time between the two.

What about 90-minute sleep cycles?

Many sleep calculators count back in 90-minute blocks so your alarm goes off between sleep cycles. A night does have several cycles of light sleep, deep sleep and REM sleep, when most vivid dreams happen. In a lab study of 17 healthy young adults, researchers found each person's cycle length was their own, and they note that cycles run anywhere from about 70 to 150 minutes, changing through the night as well. Ours doesn't try, since a calculator that only knows the clock can't know where yours end.

Should you go to bed earlier after a bad night?

Going to bed earlier is tempting after a few bad nights, and it can backfire. Extra hours in bed give you more room to lie awake, and in one of the main models behind CBT-I, that's one of the habits thought to keep insomnia going. Over weeks, lying there awake can also train you to feel alert in bed.

CBT-I, the insomnia treatment with the best evidence behind it, keeps your get-up time the same every day, weekends included, and has you go to bed only once you're sleepy. Our guides to a get-up time that doesn't move and to leaving the bed when sleep won't come go through both. If you have bipolar disorder or epilepsy, talk to your doctor before you change your sleep times.

The 7 to 9 hours describes healthy adults over months and years, and nobody hits it every night. With insomnia, worrying about the number can add to the pressure that keeps sleep away, and easing off that worry is part of CBT-I.

When is it worth seeing a doctor?

Getting 7 to 9 hours and still dozing off without meaning to is worth seeing a doctor about, and so is someone hearing you snore loudly, gasp or stop breathing in your sleep. If you're drowsy, don't drive.

How Goodmorrow coaches it

Goodmorrow picks your first habit from what's keeping you up. When the trouble is staying up too late rather than lying awake, you'll usually start on a steady get-up time, with "Same bedtime, every night" soon after. In that habit's first week, a reminder comes 30 minutes before bed, something like "Thirty minutes to 11:00. Time to start wrapping up." Once it's had two weeks, we go back over your nights and say whether we think it helped.