How Many Hours of Sleep Do I Need Each Night?

Most adults need 7 to 9 hours of sleep a night. That is the range recommended by sleep experts for healthy adults — less than 7 hours on a regular basis is linked with worse mood, weaker memory, slower reactions and poorer health, while a few people genuinely do well on 7 hours and others need the full 9. The right amount for you is the one that leaves you feeling alert through the day without an alarm clock, a mid-afternoon crash, or a heavy reliance on caffeine.

By Calcly Team · Last updated 6 November 2026 · Free guide · General information only

How much sleep you need by age

Sleep need falls as you get older, but it never disappears. Newborn babies need 14 to 17 hours a day, infants 12 to 16 hours, and toddlers 11 to 14 hours. School-age children need 9 to 12 hours, teenagers 8 to 10 hours, younger adults 7 to 9 hours, and older adults 7 to 8 hours. These are ranges, not exact targets, because sleep need varies from person to person — and it varies for the same person too. You need more sleep when you are ill, recovering from hard exercise, learning something demanding, or catching up after short nights. A good test is the holiday test: if you sleep 9 or 10 hours a night for the first few days of a holiday, you were probably carrying a sleep debt. If you settle at 7.5 hours and wake naturally, that is likely close to your real need. Children and teenagers need more than adults because their brains and bodies are still growing, and their body clocks naturally run later, which is why a teenager who cannot fall asleep before midnight is not necessarily being difficult — their biology really is on a later schedule.

Sleep works in 90-minute cycles

Sleep is not one long, even state. It runs in cycles of about 90 minutes, each moving from light sleep through deep sleep to dream sleep, known as REM sleep. A full night is usually 5 or 6 of these cycles: 5 cycles is 7.5 hours in bed and 6 cycles is 9 hours. This matters because how you feel when you wake depends less on the total hours and more on where in a cycle the alarm catches you. Waking at the end of a cycle, during light sleep, usually feels fairly easy. Waking in the middle of deep sleep can leave you groggy, confused and heavy-headed for half an hour or more, even if you slept for 8 hours. That is why 6 hours — four complete cycles — can sometimes feel better than 7 hours, which may end mid-cycle. It is also why counting cycles is more useful than counting hours alone: aim for 5 or 6 complete cycles, not just a round number of hours.

Worked example: picking your bedtime

Say you need to wake up at 7:00 AM. Allow about 15 minutes to fall asleep, then count back in 90-minute cycles. Six cycles is 9 hours, so 7:00 AM minus 15 minutes minus 9 hours is 9:45 PM the night before. Five cycles is 7.5 hours, so the bedtime is 11:15 PM. Four cycles is 6 hours, giving a 12:45 AM bedtime, and three cycles is 4.5 hours, giving 2:15 AM — both far too little for most people, but useful if you are working out the least-bad option on a very short night. For a 6:00 AM alarm the same maths gives 8:45 PM for six cycles and 10:15 PM for five cycles. The easiest way to do this for your own alarm time is our sleep calculator: enter your wake-up time and it lists every bedtime that ends a cycle, or choose “I want to sleep now” and it tells you the best times to wake up instead.

Signs you are not getting enough sleep

Short sleep is easy to miss because you get used to feeling tired and start calling it normal. The clearest signs are needing an alarm to wake up and still feeling unrefreshed, falling asleep quickly whenever you sit still, needing caffeine to get through the afternoon, and noticing your mood, patience and memory getting worse. Microsleeps — brief moments where you blank out for a few seconds, especially while driving — are a serious warning sign and mean you should not drive until you have slept. If you regularly sleep less than 7 hours and feel fine, be honest with yourself: many people who say they “only need 5 hours” are actually running on a sleep debt and have simply forgotten what rested feels like. Try a week of 8 hours in bed at a fixed time and see how the afternoons feel — the difference is often obvious within a few days.

Naps, sleep debt and catching up

A short nap can help, but length matters. A nap of about 20 minutes boosts alertness without letting you fall into deep sleep, so you wake up fairly fresh. A nap of 45 minutes or more can wake you from deep sleep and leave you groggy, and a late-afternoon nap can make it harder to fall asleep at night. As for sleep debt, you can repay some of it — a lie-in after a short week does help — but you cannot bank sleep in advance or fully repay a month of short nights in one weekend. Sleeping in by more than an hour also shifts your body clock later, which can make Monday morning worse than it needed to be. The most reliable fix is boring but effective: the same bedtime and the same wake time every day, including weekends, within about an hour. Regularity trains your body clock, and a trained body clock is what makes falling asleep quick and waking up easy.

Simple habits that protect your sleep

Good sleep is mostly about timing and light. Get bright light in the morning — daylight, or a bright room — and dim the lights in the evening, because light is the strongest signal your body clock receives. Keep the bedroom cool, dark and quiet, and use it mainly for sleep. Avoid caffeine after mid-afternoon, since it can still be active in your system 8 hours later, and keep alcohol out of the wind-down routine: it may help you fall asleep but it fragments the second half of the night. Screens are less about the light and more about the content — an argument, a stressful email or an endless feed keeps your mind alert when it should be winding down. If you lie awake for more than about 20 minutes, get up, do something calm in dim light, and return to bed when you feel sleepy rather than watching the clock. And if poor sleep lasts for weeks, or you snore heavily, gasp in your sleep or feel exhausted despite long nights in bed, speak to a doctor — those can be signs of a sleep disorder that no bedtime maths can fix.

Find your own bedtimes with our sleep calculator, and check the other side of your health with our calorie calculator and BMI calculator.

This guide is general information only, not medical advice. If poor sleep lasts for weeks or affects your daily life, speak to a qualified health professional.