How Much Sleep Do You Need?

How much by age

Sleep needs fall as we grow. Newborns sleep 14–17 hours, school-age children 9–12, and teenagers 8–10 as their body clocks shift later. Most adults settle at 7–9 hours, and older adults often at the lower end, 7–8, though they may nap. These are ranges, not targets: some people genuinely do well on 7, others need a full 9. The honest test is how you feel and function during the day.

Sleep cycles and the 90-minute rule

Sleep isn't uniform — it moves through cycles, each about 90 minutes long, from light sleep down into deep sleep and up into REM, where most dreaming happens. A full night is roughly five or six of these cycles back to back. Waking naturally at the end of a cycle, in light sleep, feels refreshed; being jolted awake in the middle of deep sleep is what leaves you groggy, even after plenty of hours.

Timing your bedtime

You can use the cycles to pick a bedtime. Start from the time you must wake, then count back in 90-minute blocks — five cycles is 7.5 hours, six is 9 — and add about 15 minutes for falling asleep. To wake at 7 a.m., that points to lights-out around 11:15 p.m. (5 cycles) or 9:45 p.m. (6 cycles). It's an estimate, since cycle length varies, but aiming for a whole number of cycles beats waking in the middle of one.

Quality matters as much as quantity

Hours in bed only help if the sleep is sound. Eight broken, restless hours can leave you worse than seven solid ones. The basics that protect quality are a consistent sleep and wake time, a dark, cool, quiet room, and easing off screens, caffeine and heavy meals in the hours before bed. If you regularly sleep enough but still wake tired, it's the quality — or a sleep problem worth checking — not just the clock.

Frequently asked questions

How many hours of sleep do I need?

Most adults need 7 to 9 hours a night; individual needs vary a little.

What is the 90-minute sleep rule?

Sleep cycles last about 90 minutes, so waking at the end of one feels less groggy.

Is 6 hours of sleep enough?

For most adults, no; regularly under 7 hours is linked to worse health and focus.