How Much Sleep Do You Need? A Guide by Age

Most adults need seven to nine hours of sleep a night, and the exact number depends on your age, your training load and how much physical recovery your body is doing. Sleep also runs in cycles of about 90 minutes, so eight hours in bed rarely means eight hours asleep. This is general information, not medical advice; sleep problems that last for weeks belong with a doctor.

The adult range: seven to nine hours

Common guidelines put most adults between seven and nine hours a night. Some people run fine on six and a half and others need nine and a half, because sleep need is partly genetic. Hard training, infection, pregnancy and night shifts each push the requirement up for weeks at a time. A Sunday lie-in repairs very little of five short nights.

Feeling fine on six hours does not prove six is enough. Sleep loss narrows your own judgement before it shows on a clock: reaction time slows while you still rate yourself as alert. Falling asleep within five minutes of lying down most nights is a fairly reliable sign of a deficit, since a rested adult usually takes ten to twenty minutes.

Sleep needs by age

Sleep need falls steeply in the first year, then slowly through childhood. The ranges below match most paediatric and adult guidelines, and they count total sleep including naps until the daytime nap is dropped between three and five years.

• 0 to 3 months - Fourteen to seventeen hours in blocks of two to four hours; newborn sleep has not yet merged into day and night patterns.
• 4 to 12 months - Twelve to sixteen hours including two or three naps, with night sleep consolidating into longer stretches from around four months.
• 1 to 2 years - Eleven to fourteen hours including one or two naps; most toddlers drop to a single afternoon nap by about eighteen months.
• 3 to 5 years - Ten to thirteen hours including one nap; dropping the nap on too little night sleep makes bedtime harder, not easier.
• 6 to 13 years - Nine to eleven hours; a school start before 8am pushes many children below this during term time.
• 14 to 17 years - Eight to ten hours; the teenage body clock shifts later by up to two hours, so a 7am alarm often cuts the night short.
• 18 to 64 years - Seven to nine hours; pregnancy, shift work and heavy training weeks add thirty to sixty minutes to the requirement.
• 65 and over - Seven to eight hours, often in a lighter, more broken pattern, with more time in bed but less asleep.

Test your own number in one week

Hold one wake time for seven days, weekend included, and do not use an alarm. Go to bed when you feel sleepy, and note each night how long you take to fall asleep.

Read the pattern at the end of the week. Falling asleep in under five minutes every night, plus a strong nap urge before 2pm, points to a shortfall of an hour or more. Taking twenty to thirty minutes to fall asleep most nights usually means your bedtime is set earlier than your body clock can manage.

The weekly average is the number that counts. One nine-hour night after five six-hour nights leaves you at about six and a half hours a night, which is close to fifteen hours owed for the week.

Two nights are enough to see a pattern if you record sleep onset time and not only hours in bed. Someone who needs nine hours but sets a seven-and-a-half-hour window is short every night and may end up convinced they are a poor sleeper when the window is the problem.

Why 90-minute cycles change the maths

Sleep cycles run about 90 minutes, mixing light sleep, slow-wave sleep and REM. Slow-wave sleep dominates the first two cycles, so the deepest physical recovery happens in the first three hours of the night.

REM lengthens toward morning, so the last cycle before waking holds the largest share of dreaming sleep. Cutting the final 90 minutes removes far more REM than the arithmetic suggests, which is one reason six hours feels worse than it looks. Setting your alarm a whole number of 90-minute cycles after lights out often reduces the heavy grogginess that follows waking out of deep sleep.

Cycle length is not identical for everyone. Most people run between 80 and 100 minutes, so a 90-minute block is a starting point to adjust from rather than a fixed rule.

Signals that need a doctor, not an app

Loud snoring with pauses in breathing, gasping or choking sounds, or waking with a dry mouth and headache are reasons to ask for a sleep assessment, because they can point to obstructive sleep apnoea. Apnoea is common, serious and treatable, and it does not improve with bedtime tweaks.

Daytime sleepiness that never lifts despite eight hours in bed, falling asleep while driving, or needing caffeine to stay awake through the morning are the same kind of signal. Insomnia lasting more than three nights a week for three months also warrants an assessment. Never stop or change a prescribed sleep medicine, or a CPAP setting, without the clinician who prescribed it.

A place to start tonight

Fix the wake time and count backwards. Seven and a half hours of sleep plus fifteen minutes to fall asleep means lights out at 10:45pm for a 6:30am alarm. Ten to fifteen minutes of daylight within an hour of waking anchors the clock, then move bedtime fifteen minutes earlier every three or four nights until you wake just before the alarm.