How long should a nap be, and when?

For most adults, the advice points to short naps. The US National Heart, Lung, and Blood Institute (NHLBI) advises adults to nap for no more than 20 minutes. Training material from CDC NIOSH, the US workplace health institute, recommends a brief nap of under 20 minutes for daytime workers and suggests setting an alarm for 15 to 30 minutes, because waking after about an hour, when you are likely to be in deep sleep, can leave you very groggy. The early afternoon, around 2 to 4 p.m., is a natural window for a nap, while in the 1 to 3 hours before bedtime it is harder to fall asleep and stay asleep. If you already find it hard to sleep at night, England's NHS advises not napping during the day. A nap helps on a sleepy day, but it does not replace enough sleep at night.

For a day after a short night, see Short on sleep but need a clear head? What should I do?. For sleepiness that lasts all day, see Always sleepy during the day? Why, and what can I do?

How long should a nap be?

Most guidance points to short naps, and the reason is what happens when you wake from deeper sleep.

What guidance says about nap length

Why the alarm is set a little longer than the nap

It usually takes a few minutes to fall asleep. NIOSH suggests an alarm of 15 to 30 minutes for a nap of under 20 minutes, so you get a short sleep without sliding into deep sleep.

What research says about "30 minutes or less"

Many workplace guides recommend naps of 30 minutes or less to avoid grogginess. A 2017 review by Hilditch and colleagues at the University of South Australia looked at the studies behind this advice. It found mixed results on how soon deep sleep starts and how strong grogginess is after short naps, and concluded that the effect depends on how much sleep a person had before the nap and the time of day they wake up. NIOSH similarly notes that grogginess after waking can last longer when you are short of sleep.

Why do I feel groggy after a nap?

That heavy, slow feeling has a name: sleep inertia.

What sleep inertia is

CDC NIOSH material describes sleep inertia as a temporary disorientation and decline in performance and/or mood after waking from sleep. It says sleep inertia usually does not last longer than 30 minutes, but can be longer if the person is short of sleep. Researchers have observed it lasting up to 2 hours.

What makes it worse

• Waking from deep sleep. NIOSH notes that waking after about 1 hour, when you are in deep sleep, can make your functioning drop considerably.
• Being short of sleep. NIOSH notes that if you are very short of sleep when you start a nap, you may reach deep sleep more quickly, so the grogginess can last longer even after a short nap.
• Napping at a time of strong sleep pressure. In night-shift workers, NIOSH describes longer sleep inertia after an hour-long nap in the early morning, around 4 to 5 a.m.

Give yourself time before important tasks

NIOSH advises allowing time for sleep inertia to pass before doing critical tasks. After a nap, allow time for the grogginess to pass, which NIOSH says usually takes no longer than 30 minutes, before driving, operating machinery or making an important decision. NIOSH also mentions bright light and washing your face as ways people restore alertness after waking.

What time of day is best for a nap?

Your body clock makes some times easier for napping than others.

The afternoon dip

CDC NIOSH material explains that in the middle of the afternoon, the body clock's push for wakefulness dips while sleep pressure has built up enough to take over. This is the sleepy spell many people feel after lunch.

If you sleep badly at night

The NHLBI advises that if you have trouble sleeping at night, you should limit naps or take them earlier in the afternoon. England's NHS goes further and advises not napping during the day in that case.

How much sleep do people in Thailand get?

Naps are one part of a day's sleep. Thai national data give a picture of how much sleep people get across the whole day.

The Thai guideline and how many adults meet it

Thailand's Ministry of Public Health issued 24-hour movement guidelines in 2017 that advise adults aged 18 to 59 to sleep 7 to 9 hours a day. An analysis of the national time-use survey of 167,577 Thai adults by Liangruenrom and colleagues found that in 2015, 56.4% met this range. The study counted sleep including naps.

Sleep time by age in the national time-use survey

A second analysis by Liangruenrom and colleagues, covering 135,824 Thais aged 10 and over in the 2009 and 2015 surveys, counted all sleep in the 24 hours, both overnight sleep and naps. People recorded their activities for one day in 10-minute blocks.

Because naps are included and people recorded their own day, these figures are higher than night sleep alone and do not show how much of the time was napping. They do show that people in Thailand sleep longer on weekends than on weekdays.

How many hours each age group needs

The US CDC recommends 7 or more hours for adults aged 18 to 60, 7 to 9 hours for ages 61 to 64, 7 to 8 hours for those 65 and over, and 8 to 10 hours for teens aged 13 to 17. For young children aged 1 to 5, its recommendations include naps.

Can a nap make up for a short night?

Only partly. A nap is a short-term help, not a swap for night sleep.

What NIOSH says

CDC NIOSH material says studies show a 15 to 20-minute daytime nap can improve alertness, and that naps are a temporary aid, not a replacement for a regular, long period of sleep.

Put night sleep first

The CDC advises going to bed and getting up at the same time every day. If you find you need a nap every afternoon, look first at how much and how regularly you sleep at night. The NHS advises against sleeping in after a bad night, and suggests sticking to your regular sleeping hours.

Trouble sleeping or too sleepy to get through the day: when should I see a doctor?

Needing a short nap now and then is common. England's NHS gives signs for when trouble sleeping is worth seeing a doctor about.

Signs to see a doctor

England's NHS advises seeing a doctor if changing your sleep habits has not helped, if you have had trouble sleeping for months, or if it affects your daily life in a way that makes it hard to cope.

Drowsy driving

The NHS advises not driving when you feel sleepy.

What to tell the doctor

A doctor may ask how often and how long you nap, how much coffee, tea or energy drinks you have, and which medicines you take regularly, so it helps to have these in mind.