How Much Sleep a Person Needs: Optimal Sleep Duration by Age

Adults generally need about 7 to 9 hours of sleep each night to restore alertness and working capacity, while newborns may sleep 20–22 hours a day. The right sleep duration is not a single fixed number — it shifts with age, nervous-system type, occupation, and health, so the amount that leaves one person refreshed can leave another tired.

Sleep is the body's fundamental restorative state, during which the brain consolidates memory, the immune and nervous systems recover, and tissues repair. Understanding how much sleep a person needs, and why the need changes across a lifetime, is the first step toward protecting both energy and long-term health.

Why the cerebral cortex needs sleep

Sleep protects the nerve cells of the cerebral cortex from exhaustion. During waking hours, countless stimuli from the outside world flood into the cortex of the brain, and each one places a load on its cells. Most stimuli that reach the cortex of an adult are of ordinary strength, but for the still-immature cortex of a child the very same stimuli act as "super-strong" — capable of rapidly driving the nerve cells toward exhaustion.

Protective inhibition and children's sleep

To prevent the nerve cells from becoming exhausted, children develop protective inhibition in the form of prolonged sleep. A newborn therefore sleeps most of the day, waking only when something strongly disturbs it — hunger, a wet bed, stomach pain, and the like. As the cerebral cortex matures and grows "stronger," the need for long sleep diminishes because the cortical cells become more resistant to external stimuli. This maturation explains why sleep requirements fall so sharply through infancy and childhood.

Optimal sleep duration by age

Recommended sleep amounts drop steadily from infancy into old age, and modern guidance from bodies such as the National Sleep Foundation and the American Academy of Sleep Medicine broadly matches the classic pediatric norms. The total daily sleep time of infants is:

• in the first months of life — 20–22 hours per day;
• from 1 year — 16–17 hours;
• from 2–3 years — 14–15 hours;
• from 4–5 years — 13 hours;
• from 6–7 years — 12 hours per day.

There is still no full consensus on hygienic sleep norms for people of different ages. N. I. Krasnogorsky, a pupil of I. P. Pavlov who worked for many years on children's sleep, considered it necessary to hold children's sleep to defined norms, with the following principles in mind:

• For physically weakened, nervous, and insufficiently balanced children these norms should be increased.
• Depending on age, a person needs either single (monophasic) or multiple (polyphasic) sleep.
• Daytime sleep is recommended for all children up to 7 years of age.
• For weakened, nervous children with heightened fatigability, daytime sleep is recommended at older ages as well.
• Among adults, only in old age is an after-dinner nap advisable.

Sleep norms for infants

Infant sleep is spread across the day and night rather than concentrated at night, and newborns cycle between sleep and brief waking every few hours. Their sleep is dominated by active (REM-like) sleep, which supports the rapid brain development of the first year. Because their circadian rhythms are not yet established, newborns do not distinguish day from night — a pattern that consolidates gradually over the first several months.

Sleep norms for preschool and school-age children

Preschoolers (roughly 3–5 years) need about 10–13 hours of sleep including naps, while school-age children (6–12 years) need about 9–12 hours. As the classic norms above show, the total falls to around 12–13 hours by ages 6–7. Consistent bedtime routines and adequate deep sleep matter especially here, because slow-wave sleep is when growth hormone is released and the day's learning is consolidated.

Adolescent sleep and the shift in circadian rhythm

Teenagers need roughly 8–10 hours of sleep, but their circadian rhythms shift later during puberty, delaying the natural time of sleep onset and waking. This biological delay, combined with early school start times, screen time, and social demands, leaves many adolescents chronically short of sleep. The mismatch between a teenager's internal clock and the external schedule is one of the most common causes of daytime sleepiness in this age group.

Recommended sleep duration for adults

An adult usually sleeps 7 to 9 hours a night, and healthy adults rarely need less than 7. Depending on lifestyle (more on this: Which types of men, Which types of women), nervous-system type, occupation, and workload, some people sleep for shorter periods — from 6 down to about 5 hours a day. Sleep researchers distinguish short sleep, generally defined as fewer than 7 hours per night, from adequate sleep, and consistently short sleep is linked to higher risk of chronic disease and earlier mortality. Peter the Great, for example, is said to have slept no more than 5–6 hours a day.

Age-related changes in sleep among older adults

Older adults still need about 7–8 hours, but their sleep becomes lighter, more fragmented, and less rich in deep slow-wave sleep. They tend to fall asleep and wake earlier, wake more often during the night, and rely more on daytime naps to make up for interrupted nighttime rest. These changes are a normal part of aging rather than a disease, though they can be worsened by medications, pain, and sleep disorders that become more common with age.

Single and multiple sleep

Sleep can be monophasic — taken once at night — or polyphasic, spread across the day in more than one period. Which pattern a person needs depends largely on age: young children require multiple sleep periods, while most healthy adults consolidate their rest into a single nighttime block.

Daytime sleep in children and adults

Daytime napping is recommended for all children up to age 7, and for weakened or nervous children beyond that age. For adults, a short after-dinner nap is generally advised only in old age. Well-planned power napping — a brief nap of about 10–20 minutes — can restore alertness in adults without causing the grogginess that follows longer naps, and segmented sleep with a daytime rest has been a normal cultural practice in many parts of the world.

Sleep stages and their duration

Sleep is not uniform: it is built from repeating cycles, each lasting roughly 90 minutes and made up of several stages. Sleep scientists divide these into non-REM (NREM) sleep and REM sleep. NREM sleep itself has three stages — N1, N2, and N3 — and together with REM they form the architecture of a night's rest, which can be mapped on a chart called a hypnogram.

• Stage N1 (light sleep): the brief transition from wakefulness to sleep, lasting only a few minutes, when muscles relax and the sleeper is easily woken.
• Stage N2: a deeper, longer stage that makes up the largest share of the night, in which body temperature drops and heart rate slows.
• Stage N3 (deep sleep): slow-wave sleep, the most restorative stage, when the body carries out its heaviest physical recovery.
• REM sleep: the stage of vivid dreaming and rapid eye movement, essential for memory and emotional processing.

A person passes through four to six of these cycles per night. Early cycles contain more deep sleep, while REM periods grow longer toward morning — which is why the last hours before waking are dream-rich. Sleep specialists such as Eric Suni and Abhinav Singh of the Sleep Foundation emphasize that the balance of these stages matters as much as total hours.

Deep (slow-wave) sleep and its restorative function

Deep sleep, or stage N3, is when the body repairs itself and grows. During slow-wave sleep the brain produces large, slow delta waves, blood pressure falls, and the body releases growth hormone that drives tissue repair, muscle building, and immune strengthening. Deep sleep should make up roughly 13–23% of a healthy adult's night. It is also the hardest stage from which to be woken, and disturbances that arise from it — such as sleepwalking and night terrors — belong to a class of sleep disorders known as parasomnias.

REM sleep and its link to dreaming

REM sleep is the stage most closely tied to vivid dreaming and to memory consolidation. During REM the brain becomes highly active — nearly as active as during waking — while the major muscles are temporarily paralyzed to keep the sleeper from acting out dreams. REM supports learning, creativity, and the processing of emotions, and its share of the night grows in the later cycles. Newborns spend far more of their sleep in REM-like active sleep than adults do, reflecting its role in brain development.

Brain activity and eye movements across sleep stages

Each stage of sleep has a distinct signature of brain activity and eye movement, which is why sleep is studied with an electroencephalogram (EEG) as part of a polysomnogram. As sleep deepens through NREM, brain waves grow slower and larger and the eyes are still; in REM, brain waves speed up and the eyes dart rapidly beneath closed lids — the movements that give the stage its name. A sleep study, or polysomnogram, records these signals together with breathing, heart rate, and muscle tone to diagnose sleep disorders such as sleep apnea, insomnia, narcolepsy, and restless leg syndrome.

Individual differences in sleep duration

Although sleep is a vital biological need, its required length varies widely between individuals of different ages, temperaments, and professions. The outstanding Russian scientist V. M. Bekhterev also slept very little, which did not prevent him from working and creating productively until the age of 76.

Famous people who slept little (Peter the Great, Bekhterev, Edison)

Some notably productive people managed on very short sleep because their inhibition was unusually deep and complete. The American inventor Thomas Edison argued that four hours of sleep were enough for him, though he admitted he was not averse to dozing during work in the laboratory. This is explained by the fact that the inhibition developing in some people, lasting a few hours, is so strong and complete that it suffices to restore energy expenditure and normal function of the brain cells. Thus, although sleep is necessary for a person and is a vital need of the body, its duration differs for people of different ages, characters, and professions and varies within very wide limits.

Factors that affect the need for sleep

How much sleep a person needs is shaped by the nervous system, occupation, diet, alcohol, exercise, and general health. No single factor sets the total; they combine, which is why two people of the same age can have genuinely different requirements.

Nervous-system type and the nature of one's work

The type of nervous system and the character of a person's profession strongly influence sleep need. People whose work is mentally intense or emotionally taxing, and those with a more excitable nervous system, often require more restorative sleep, while others with deep, efficient inhibition recover in fewer hours. The demands of the job — night shifts, irregular hours, high concentration — further alter both how long and how well a person sleeps.

How diet affects sleep quality

Dietary habits have a direct effect on sleep quality. Heavy meals, caffeine, and sugar close to bedtime can delay sleep onset and fragment the night, while going to bed hungry can be equally disruptive. Eating the main meal earlier in the evening and keeping caffeine to the first half of the day help protect the deep and REM stages that make sleep restorative.

How alcohol affects sleep cycles

Alcohol disrupts the normal cycle of sleep even though it can make a person fall asleep faster. It suppresses REM sleep in the first half of the night and causes fragmented, lighter sleep and more awakenings later, so the overall rest is shallower and less restorative. Regular drinking before bed therefore reduces sleep quality even when total time in bed looks adequate.

Physical activity and the timing of exercise

Regular physical activity improves sleep quality and increases the proportion of deep sleep, but its timing matters. Exercise earlier in the day supports a healthy circadian rhythm, while vigorous training too close to bedtime raises body temperature and alertness and can delay sleep onset. For most people, finishing intense workouts at least a couple of hours before bed gives the best balance.

Sleep hygiene: practical recommendations

Sleep hygiene is the set of daily habits and environmental conditions that make good sleep easier to achieve. Clinicians at organizations such as the Cleveland Clinic and the Sleep Foundation recommend a consistent set of measures that most people can apply without medication:

• Keep a consistent bedtime and wake time, even on weekends, to stabilize the circadian rhythm.
• Optimize the bedroom environment: cool, dark, quiet, and comfortable.
• Limit screen time before bed, since blue light suppresses the sleep signal.
• Avoid caffeine and alcohol in the hours before sleep.
• Get daylight exposure and regular exercise during the day.
• Reserve the bed for sleep, building a clear association between bed and rest.

When persistent trouble sleeping continues despite good habits, it is worth seeking medical help. Ongoing insomnia, loud snoring with pauses in breathing, or overwhelming daytime sleepiness can signal a treatable sleep disorder, and a sleep specialist may recommend a sleep study to diagnose the cause and guide treatment.

How long can a person go without sleep

A person cannot truly go without sleep for years, even in famous cases that appear to show it — some form of partial sleep is always present. The very important question of how long a person can do without sleep without harm to health arises largely from various press reports about people said to have gone years or decades without sleeping.

• In London, a certain Sidney Edward lost his sleep on a July night in 1941, when his fiancée was killed during an air raid. Sidney witnessed the tragedy, and this psychological shock deprived him of sleep forever. He said of himself:

  — I see no difference between day and night. For me it is only an endless chain of constantly changing hours. While it is still light, I try to fight my affliction. First I work in the shop, then I go to the neighboring tavern. But when the lights go out, real torment begins for me. I am left completely alone and feel as disconsolate as a shipwreck survivor in the open sea.

• An accident deprived the Spanish worker Valentín Medina Pover of sleep. He has been awake for 12 years. Despite his age, Pover works at a machine-building plant not only on the day shift but also on the night shift. His comrades call him "the human perpetuum mobile."
• For 20 years, it is said, the Portuguese Allenalio Rosa Mareiro "has had no need of an alarm clock."
• One case is of special interest. In the modest village of Vlagai (Yugoslavia) lives the peasant Franjo Mikulić, who does not know what sleep is. In the spring of 1942, when the boy was not yet 7, a hand grenade exploded near him. The child froze with fear, then ran home. That evening he tried in vain to fall asleep — sleep did not come.

Weeks, months, and years passed, but he still could not fall asleep. The doctors who examined him maintained that Franjo was completely healthy. He finished primary school without difficulty and then took up ordinary agricultural work.

Time did its work, Franjo says, and over these years I have grown used to insomnia. I am quite healthy. But I would be lying if I said I feel no discomfort at all: it is not easy to spend whole nights in bed without sleep.

In summer it is easier for me, especially when the nights are warm. I walk about, trying not to disturb my family. After such walks I feel ready to get to work. As a rule, I almost never feel tired.

In the army Franjo turned out to be an exemplary soldier and served his full term. Admittedly, the hardest time for him was when sleep-time came. He had to tell his superiors about his trouble. Franjo was immensely happy when he was allowed to go on night watch almost every evening.

Moreover, Mikulić possesses a phenomenal memory: without pencil and paper he performs the four basic arithmetic operations. He still remembers the serial numbers of the rifles of all the soldiers in his platoon, though so many years have passed since demobilization.

The platoon commander tested his memory more than once: he would pick up a rifle and name the owner, and Franjo would answer the number without error. He multiplies six-digit numbers in his head in a few seconds.

— I have heard, says Franjo, that someone set a world record by fairly quickly calculating two thousand years ahead when the leap years will fall and determining the dates of the great holidays. I do not know whom to turn to, but I am sure I can easily beat his record and, in a short time, work out in my head all these dates not two thousand but ten thousand years ahead. In a hundred-year calendar I have already found about 30 major errors.

Franjo Mikulić connects his abilities with the tragic event that deprived him of sleep forever. Until then he differed in no way from his peers.

Although all the cited examples of prolonged absence of sleep concern people who suffered various injuries and diseases of the brain, they nonetheless require explanation — first of all, an answer to the question of whether they contradict the most important propositions of I. P. Pavlov's theory on the essence and causes of sleep (more on this: Theories of sleep).

After all, science asserts that a person cannot live without sleep, because sleep protects the nerve cells from exhaustion and overwork and saves them from death. But what about Franjo Mikulić? Since he is awake all the time, his nerve cells are in constant excitation, and yet they do not die — the doctors recognize him as healthy, and he himself feels well.

How can such a phenomenon be explained? During sleep not all cells "sleep." The same is true during waking: not all 14 billion cells are excited and active at once. Some portion of them rests and frees itself of the accumulated harmful residues of metabolism.

At the same time, this portion of cells takes in new nutrient material needed to restore its normal activity. This means that a separate group of nerve cells "sleeps" even while the person is awake, and to some degree this group of cells is protected from exhaustion and death.

Such "partial" sleep can take various forms. There are known cases where inhibition affects only the motor areas of the cortex without touching consciousness.

For example, in catalepsy — a condition in which the patient does not move and seems fettered while consciousness is preserved. And conversely, it happens that consciousness is inhibited while motor function is preserved. The patient, as if in a sleeping state, walks about the room, performs certain complex actions, and then, on waking, remembers nothing and can report nothing about their behavior during the sleepwalking.

Something similar probably happens with Franjo. His consciousness is always clear (though, to assert this, one would have to observe him carefully and continuously rather than rely on his personal statement alone), but partial inhibition sets in, and some groups of brain nerve cells are inhibited and resting. Franjo Mikulić, in all likelihood, does sleep, cannot help sleeping, though he does not suspect it.

Sometimes patients come to psychiatrists categorically declaring that they have not slept at all for several months, and sometimes even years. On careful questioning and observation, however, it turns out that sleep — partial and fragmentary though it is — does occur, but they lack the familiar sensation of sleep.

And what can be said of Franjo Mikulić's phenomenal memory and mathematical abilities? There are no grounds to connect them with his chronic insomnia. There is no doubt that the Yugoslav peasant could have become a gifted mathematician even if he had not suffered psychological trauma in childhood and his sleep had been as normal as that of most healthy people.

Recovery and growth of the body during sleep

Sleep is when the body carries out much of its physical recovery, repair, and — in children — growth. During deep slow-wave sleep the body releases growth hormone, rebuilds tissue, strengthens the immune system, and clears metabolic waste from the brain, while the nervous system consolidates the day's learning. Because so much restoration is concentrated in sleep, adequate rest is one of the body's most powerful tools for disease prevention, and long-term sleep deprivation shows up as fatigue, impaired concentration, weakened immunity, and heightened risk of chronic illness. An adult regulates the length of their own sleep, since sleep in many cases replaces medicine for the body.