How is Sleep Debt Calculated and Can you Repay It?

Healthy Sleep Practices

Tammy George

woman with her head on the desk and eyes closed, looking burnt out

Sleep. Few of us get the recommended hours of shut-eye daily. What happens if we’re constantly cheating ourselves of valuable sleep? Our bodies go into sleep debt. But the good news is you can repay some of the debt. 

What is Sleep Debt?

Sleep debt is the cumulative effect of not getting enough sleep over a number of days. Each day that the sleep debt builds, more sleep is needed to ‘pay down’ the sleep debt. So a person who needs eight hours of shut-eye a night but only gets six hours for three nights in a row has a sleep debt of six hours. Shift workers are at a higher risk of sleep debt but the rest of the population blames watching TV, long commute or work hours, socialising and relaxing for a lack of sleep. 

Impact of Sleep Debt

As sleep debt builds, a person’s brain and body function deteriorate. The physical impact on the body from not enough sleep can include fatigue, hallucinations, increased pain, and even death through accidents. The long-term impact of chronic sleep deprivation includes obesity and heart disease. Sleep deprivation can impact mood, energy levels, short-term memory, poor concentration, and brain fogginess, and can contribute to anxiety, depression and irritability. 

Repaying Sleep Debt

The good news is you can repay short-term sleep debt by getting extra sleep. You don’t need to repay every hour of sleep because you sleep more deeply when you’re sleep deprived. However, catching up on sleep can take time. One hour of sleep debt can take a few days to recover from if you have an extra 20 minutes of sleep per night. It can take more than a week to eliminate sleep debt. However, if your sleep debt has been accumulating for months, you can’t pay back all that missed sleep. Some cognitive and physical effects of lost sleep can’t be reversed.

Most people catch up on missed sleep by:

  • Sleeping in on the weekends
  • Taking a nap during the day
  • Going to bed earlier or sleeping late     

A short 20-minute daytime nap may not make a big dent in the sleep debt but it can make you feel refreshed and better able to learn and concentrate for the rest of the day.

However, sleep debt and catching up isn’t a good practice to get into as it can mess up your circadian rhythm. A good circadian rhythm encourages consistent and restorative sleep. A poor internal clock can cause sleep problems including insomnia. The circadian rhythm has been connected to metabolism and weight by regulating blood sugar levels and cholesterol. It is thought that the circadian rhythm may also have a big impact on the immune system and plays a role in preventing cancer.

How to Avoid Sleep Debt

For some people, sleep comes easy and they always get their recommended amount of shut-eye. For others, falling asleep and going to bed on time is a struggle. It can take consistent effort and a routine for them to get enough sleep.  

  • Try to go to bed and get up at roughly the same time each day
  • Keep a sleep diary to track your sleep pattern and make notes of sleep problems
  • Make an appointment to see your doctor if you’re struggling to fall asleep or stay asleep
  • Go to bed when you’re tired
  • Have a bedtime routine such as a warm shower and focusing on your breathing
  • Turn off the TV and electronic devices one hour before bed
  • Cut out caffeine in the afternoon and evening if you struggle to fall asleep

woman laying in bed yawning while on her phone

FAQs on Sleep

I struggle to find time to get eight hours at once, can I split my daily sleep needs?

Split-shift schedules refers to breaking your daily sleep requirements into two or more sessions. This has been trialled for shift workers to avoid working long shifts at night when they would normally be asleep. This may be beneficial for getting more sleep in a 24-hour period. However, shorter periods of sleep mean your body may not be getting enough deep, restorative sleep. REM (Rapid Eye Movement) sleep happens 90 minutes after you fall asleep and later REM stages get longer. If you’re only having four hours of sleep at a time, you may spend more time in light sleep stages and less time in deep sleep which may impact your body's restorative process. 

I can function fine on five or six hours of sleep a night, would I have sleep debt?

The recommended amount of sleep for an adult is seven to nine hours but many people have far less and don’t feel sleep deprived. Even if you feel fine, a lack of sleep can have biological impacts that you may not be aware of for many years. Extra kilos could be to blame, but lack of sleep could also increase the risk of diabetes and cardiovascular disease in the future.

How much sleep do I need?

Different stages of life have differing sleep requirements. A newborn baby before the age of three months needs 12-18 hours per day. Between four and eleven months, their sleep needs drop to 12-15 hours. 

Toddlers aged one to two years need 11-14 hours, while preschoolers between three and five years require 10-13 years. From the ages of six to thirteen, school children need 9 to 11 hours. Teenagers tend to need 8 to 10 hours, while eighteen to twenty-five-year-olds need only 7-9 hours.

This amount of recommended sleep continues right through until the senior years. By retirement age, a person needs around seven to eight hours of shut-eye per night.

Do I need to go to sleep at a set time to avoid sleep debt?

Some people go to bed early and get up early while others are night owls and prefer to sleep later. Everyone has a different circadian rhythm. As long as you are getting an adequate amount of sleep and your bedtimes don’t change drastically day-to-day, the time you go to bed doesn’t matter. 

I struggle to fall asleep quickly so I’m not getting enough sleep, what can I do? 

You’re not alone. Thousands of Australians struggle to get enough sleep. Try different ways to improve your sleep routine. If you’re still struggling, see your doctor about a sleep study in case you need treatment for a sleeping disorder.    

I’m not sure if I suffer from sleep debt or not? 

Some people don’t know how much sleep they’re getting because they don’t take note of the time they go to bed, get up and roughly how long it took them to fall asleep. Try to note down your bed times in a diary or wear a fitness tracking device to bed that tells you how long you slept.   

If you are consulting a healthcare professional about your sleep, ask about the possibility of being referred to a sleep specialist who may be able to organise an at-home sleep study. Certain hospital cover policies will cover your visit to a sleep specialist, so take a look at your options today. 


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Tammy George

Please note: Tammy's blog is general advice only. For further information on this topic please consult your healthcare professional.

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