How Much Sleep Do I Need?

Medically Reviewed by Sabrina Felson, MD on August 22, 2022

Written by WebMD Editorial Contributors 5 min read

How Many Hours of Sleep Do You Need?

The amount of sleep a person needs depends on many things, including their age. In general:

But experts say that if you feel drowsy during the day, even during boring activities, you haven't had enough sleep.

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Sleep Deprivation and Sleep Debt

The amount of sleep a person needs goes up if they’ve missed sleep in previous days. If you don’t have enough, you’ll have a "sleep debt," which is much like being overdrawn at a bank. Eventually, your body will demand that you start to repay the debt.

We don't really adapt to getting less sleep than we need. We may get used to a schedule that keeps us from getting enough sleep, but our judgment, reaction time, and other functions will still be off.

Why You Need REM Sleep and Deep Sleep

There are four stages of sleep, based on how active your brain is. The first two are light.

Stage three is “deep sleep,” when your brain waves slow down and it’s harder for you to wake up. During these periods, your body repairs tissues, works on growth and development, boosts your immune system, and builds up energy for the next day.

Rapid eye movement (REM) sleep, or stage R, usually starts about 90 minutes after you fall asleep. Brain activity increases, your eyes dart around quickly, and your pulse, blood pressure, and breathing speed up. This is also when you do most of your dreaming.

REM sleep is important for learning and memory. It’s when your brain handles information you’ve taken in during the day and stores it in your long-term memory.

Signs of Sleep Deprivation

Common signs that you haven’t gotten enough sleep include:

How to Know if You’re Getting Enough Sleep

To find out whether you’re getting enough sleep at night, ask yourself:

The Effects of Sleep Deprivation

Too little sleep can cause:

Studies make it clear that sleep deprivation is dangerous. People who missed some sleep before getting into a driving simulator or doing a hand-eye coordination task perform as badly as or worse than people who had been given alcohol.

Sleep deprivation also changes how alcohol affects your body. If you drink while you’re tired, you’ll be more impaired than somebody who got enough rest.

Driver fatigue caused about 83,000 car accidents between 2005 and 2009 and 803 deaths in 2016, according to the National Highway Traffic Safety Administration.

Some researchers say the numbers are actually much higher. Since drowsiness is the brain's last step before falling asleep, driving while drowsy can -- and often does -- lead to disaster. Stimulants like caffeine can’t stop the effects of severe sleep deprivation.

The National Sleep Foundation says you’re probably too drowsy to drive safely if you:

How to Get the Sleep You Need

Healthy habits can help you sleep better and longer.