How much sleep do you need?

Article 8 min

You will be able to: State the recommended sleep for your age, tell time in bed from time asleep, and work out your lights-out window.

The numbers by age

The CDC publishes one simple table, based on expert panels. Here it is for teenagers and adults, with the NHS range alongside for adults:

Younger children need a lot more: 9 to 12 hours at ages 6 to 12, 10 to 13 hours at ages 3 to 5, and more again for toddlers and babies, including naps.

How many people actually manage it?

What about more than 9 hours? The expert statement says it may be right for young adults, for people recovering from a sleep debt, and for people who are ill. For everyone else, the evidence is not clear. If you regularly need a lot more or a lot less than the range, that is worth mentioning to your GP.

Time in bed is not time asleep

Here is where many people go wrong. They go to bed at 23:00, get up at 06:00 and count seven hours. But those seven hours are time in bed. Some of it goes on falling asleep, and it is normal to wake briefly now and then in the night.

Sleep researchers look at four simple markers of good-quality sleep. According to an expert panel convened by the US National Sleep Foundation, signs of good sleep in healthy adults include:

• falling asleep within 30 minutes of trying;
• waking no more than once in the night;
• being awake for no more than about 20 minutes in total after first falling asleep;
• being asleep for at least 85% of the time you spend in bed. This is called sleep efficiency.

So if you need 7 hours of actual sleep, you will usually need a bit more than 7 hours in bed. Your diary will show you how much more.

Your number is personal

The ranges are for groups. Inside them, people differ. The best guide to your own need is a mix of two things: how long you actually sleep when you give yourself the chance, and how you feel and function in the day. That is exactly what your diary will record this week.

Work out your lights-out window

Now turn the numbers into a time. Enter the time you need to get up and how long it usually takes you to fall asleep. The calculator counts backwards and gives you a window for switching the light off.

The default of 15 minutes to fall asleep is only a starting guess. Change it to match your own nights, and update it after a week of diary entries. The window does not allow for time awake in the night: if you usually lie awake for a while after first falling asleep, switch the light off a little earlier (in good-quality sleep that is 20 minutes or less in total).

Quick check (3 questions)

Sources

• CDC, About sleep (recommended hours by age)
• Watson et al. (2015), AASM and SRS joint consensus, PubMed 26039963; AASM summary (PDF)
• NHS, Insomnia; NHLBI, How much sleep is enough?
• Ohayon et al. (2017), National Sleep Foundation's sleep quality recommendations, Sleep Health 3(1): 6-19, PubMed 28346153; Sleep Foundation, How to determine poor-quality sleep
• Windred et al. (2024), Sleep 47(1), PubMed 37738616
• Liu et al. (2016), MMWR 65(6): 137-41, PubMed 26890214

Next: a quick body-clock check

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