How sleep debt is calculated
Example: you need 8 hours, and this week you slept 6, 6½, 7, 6, 5½, 8 and 9 hours: 48 hours in total, against 56 needed. That's a sleep debt of 8 hours, an average of 6 h 51 min a night, and 5 of 7 nights came up short.
Count actual sleep, not time in bed. If it takes you 20 minutes to fall asleep or you wake in the night, subtract that time. A sleep tracker or a simple diary for a week gives a better figure than a guess.
How much sleep you need, and catching up
Sleep experts recommend at least 7 hours a night for adults, and many people feel and perform best at 7½ to 9. Teens need 8 to 10 hours. Regularly getting less is linked to poorer concentration and mood, and over the long term to higher risks of weight gain, high blood pressure and diabetes.
A short debt from one bad week can be repaid by adding about an hour a night for several nights, ideally by going to bed earlier so your wake time stays the same. One long lie-in at the weekend helps a little but shifts your body clock, which makes Sunday night and Monday morning harder. Chronic short sleep can't be fully made up on weekends; the fix is a schedule that fits enough sleep in every night. If you sleep enough but still feel tired, or snore loudly, talk to a doctor about a sleep disorder.
Frequently asked questions
What is sleep debt?
The gap between the sleep you need and the sleep you get, added up over several nights. Sleeping 6 hours a night when you need 8 builds 14 hours of debt in a week.
Can you catch up on lost sleep?
Partly. A few nights with an extra hour can repay a short-term debt. Long-term sleep loss can't be fully made up with weekend lie-ins, which also disrupt your body clock.
How much sleep do adults need?
At least 7 hours a night, according to the CDC and the American Academy of Sleep Medicine. Some people need up to 9.
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