What is Sleep Debt and How to Pay it Back? Sleep MD Explains

Sleep debt is the running total of how much sleep you’ve missed out on recently. If you don’t get enough sleep, you’ll build up sleep debt, and this can lead to everything from low energy to trouble focusing, weight gain to heart disease. 

Below, we’ll dive into everything you need to know about sleep debt, including what it is, how to avoid it, and how to pay it back. Plus, we’ll share how the RISE app acts as a sleep debt calculator, working out how much sleep debt you have and keeping track of it as you pay it back.

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Sleep debt is how much sleep you owe your body. It’s measured against your sleep need, which is the genetically determined amount of sleep you need each night. 

For example, if you need seven hours of sleep, but you only get six hours, you’ll wake up with sleep debt. And if you continue to not get enough sleep, your sleep debt will keep building up. 

There are two types of sleep debt to be aware of: 

• Acute sleep debt: This is short-term sleep debt. At RISE, we measure this over the last 14 nights. This happens when you didn’t get enough sleep last night, or if you’ve missed out on sleep at some point over the past two weeks. 
• Chronic sleep debt: This is long-term sleep debt that’s built up over months and years. This happens when you spend your 20s only getting six hours of sleep when you need eight, for example. 

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Expert tip: Sleep scientists agree sleep debt is the most useful sleep score out there for predicting how you’ll feel and perform on a given day. We argue you don’t need to worry about time spent in deep sleep, REM sleep, or even sleep quality scores provided by apps and wearables. Instead, focus on your overall sleep duration and keeping your sleep debt low to feel your best.  

RISE works out how much sleep you need and how much sleep debt you have. 

RISE users on iOS 1.202 and above can click here to view their sleep debt.

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Sleep debt can lead to both short-term and long-term symptoms, including low energy, poor mood, worse mental performance, and mental and physical health issues. 

Short-term sleep debt can lead to: 

• Daytime sleepiness 
• Reduced attention span and focus 
• Brain fog 
• Irritability 
• A weakened immune system (a 2023 study found there’s a 27% increased risk of infection in those who get less than six hours of sleep)
• Digestive issues 
• Microsleeps and falling asleep while driving 

Long-term sleep debt can lead to: 

• Diabetes 
• Weight gain and obesity 
• Cardiovascular disease 
• High blood pressure
• Anxiety
• Depression 
• Having multiple serious health conditions (a 2022 study found sleeping for five hours or less a night at ages 50, 60, and 70 was associated with a high risk of having two or more chronic diseases like cancer and heart disease)
• Early death 

These are the common symptoms and risks of sleep debt, but everyone reacts differently to not getting adequate sleep. How much we suffer from sleep deprivation may be a genetic trait, too, and it’s not related to how much sleep we need. 

And sleep research suggests not everything is impacted to the same extent. How your mental performance is impacted by sleep debt may be different to how your alertness levels are impacted, for example. 

Plus, physiologically, our bodies may react differently to short-term and long-term sleep deficits. More research needs to be done on the impacts of both.

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If you’re feeling sleepy, irritable, and unfocused during the day (outside of your natural dips in energy, such as during the afternoon slump), you may have sleep debt. But it’s not always easy to tell as we adapt to sleep loss. 

One study found people who thought they got enough sleep slept for more than three hours longer than usual when they were given the chance to sleep for 12 hours. And another study found participants were largely unaware of their cognitive performance decreasing as they built up sleep debt. 

Beyond this, it’s impossible to know if you have sleep debt without knowing your sleep need — and many of us simply don’t know. 

To help you know once and for all, RISE works out your sleep need and whether you’re carrying any sleep debt. The app automatically keeps track of your sleep debt each night, so you can easily see if it starts creeping up or if you’re paying it back. 

We’ve covered more on how much sleep debt you have here. 

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Sleep debt is calculated by subtracting the amount of sleep you’ve had recently from the amount of sleep you need. If you’ve had less sleep than you need, you’ll have sleep debt.

At RISE, we calculate your sleep debt over the past 14 nights. But we don’t just add up the hours of sleep you’ve lost. 

We put more weighting on last night’s sleep — 15% per RISE algorithms — as it has the largest impact on how you feel and function today. That means 85% of your sleep debt comes from the previous 13 nights of sleep, with more recent days having more weighting. 

Luckily, you don’t have to work all this out yourself. RISE acts as a sleep calculator, working out how much sleep you need, automatically tracking your sleep times, and then calculating how much sleep debt you have each morning. 

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In simple terms, sleep debt is caused by getting less sleep than you need. That can happen if you don’t spend enough time asleep, you sleep at the “wrong times” (like if you’re a shift worker), or your sleep is disrupted throughout the night. 

Here’s what leads to sleep debt: 

• Your personal life: Long work hours, kids, Netflix, or late-night drinks with friends can cut into your sleep time. 
• Shift work: Both working at night and working rotating shifts. 
• Jet lag: When you fly across time zones and your body clock takes a while to catch up. More on what jet lag is here.
• Sleep disorders: Like insomnia, sleep apnea, and restless leg syndrome.
• Medical conditions and illnesses: Like chronic pain, COVID, and mental health issues like depression. 
• Poor sleep hygiene: This includes drinking coffee too late in the day and eating too close to bedtime. 
• Stress and anxiety: RISE users say these are the biggest barriers stopping them from getting a good night’s sleep.
• Medications: Such as cold meds, antidepressants, and blood pressure medications.  
• Disruptions in your bedroom: Such as when your bedroom is too hot, too loud, or too bright. 
• Hormones: You may struggle to get the sleep you need when on your period, pregnant, or going through menopause. 

Figuring out what’s causing your sleep debt is key to stopping it from building up more and helping you pay it back. 

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You can repay sleep debt to get more energy and improve your health and mental performance. 

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There’s substantial scientific evidence to back this up. One key study on the topic saw participants only getting five hours of sleep for seven consecutive nights, followed by two recovery nights. Their sleepiness, mood, and cognitive performance, like reaction time, took a hit while sleep deprived. But they bounced back after the two recovery nights.  

More recent studies have similar findings. A 2023 study found those who paid down sleep debt at the weekend had a lower risk of high cholesterol compared to those who didn’t catch up on sleep. 

And yet another study found the mortality rate of those who slept for five hours or less during the week, but got nine hours of sleep or more on the weekends, was the same as those who consistently got seven hours of sleep. 

The study concluded, “long weekend sleep may compensate for short weekday sleep.” Although more research needs to be done to be sure of this. 

But everything may not bounce back when you pay back sleep debt.  

For example, one study suggests certain aspects of your mental performance may not recover from a lack of sleep. 

In the study, participants got six hours of sleep for six nights and then 10 hours of sleep for three nights. Both sleepiness and IL-6 (an inflammatory compound) increased during the six-hour nights, but returned to normal after the 10-hour recovery nights. 

Cognitive performance, however, took a hit when participants became sleep deprived and didn’t bounce back. 

In another study, weekend recovery sleep didn’t prevent the insulin sensitivity and weight gain that short sleep can cause.

It’s hard to tell if these findings show that some effects of sleep deprivation can’t be undone, or whether participants simply didn’t get enough sleep to fully recover. In the weight loss study, for example, participants only got an extra hour or so of sleep over the weekend, which may not have been enough to pay back their sleep debt.  

We’ve covered more on whether you can catch up on sleep here, including why there’s a common myth that you can’t. 

Heads-up: While it looks like you can repay short-term sleep debt, it’s not clear yet whether you can recover from chronic sleep deprivation. More research needs to be done. 

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We recommend aiming for under five hours of sleep debt to maximize your health, energy levels, and productivity. 

Research shows when you’ve got five hours of sleep debt, your mental performance is very close to what it would be with zero hours of sleep debt.

And while having no sleep debt at all is great, it’s also unrealistic. And it’s stressful, too. You’ll worry about every minute of missed sleep, which could, ironically, lead to more sleep debt as anxiety can keep you up at night. 

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You can recover from sleep debt by getting more sleep than you usually need. Do this by taking naps, heading to bed a little earlier than usual, or sleeping in a little later. 

Depending on how much sleep debt you have, you may not be able to pay it back in one go. Keep chipping away at your sleep debt whenever you can to start seeing the benefits.

Here’s more on how to repay sleep debt. 

Find Out Your Sleep Need

To get more sleep than your body needs, you first need to know how much that is exactly. And contrary to popular belief, it’s not simply eight hours of sleep for everyone. 

When we looked at the sleep needs of 1.95 million RISE users aged 24 and older, we found the median sleep need was eight hours. But sleep needs ranged from five hours to 11 hours 30 minutes.

RISE works out your sleep need using sleep-science-based models and a year’s worth of your phone use data. You’ll then get a number in hours and minutes to aim for each night. 

RISE users on iOS 1.202 and above can click here to view their sleep need.

Take Naps 

Naps are a great way to chip away at your sleep debt and make up for lost sleep at night.  

One study found taking a two-hour nap after a night of total sleep deprivation can boost alertness and performance, and it can even reverse the increased cortisol (the stress hormone) the all-nighter causes.

But you need to be smart about napping. Avoid napping too close to bedtime or for too long — think more than 90 minutes, unless you’re extremely sleep deprived (like after an all-nighter as in the study above). Long or late naps run the risk of reducing your sleep pressure (the urge to sleep) so much that you can’t fall asleep at bedtime. This can lead to more sleep debt, not less. 

Expert tip: Keep naps short and nap during your afternoon dip in energy (RISE can tell you when this will be each day). This should help you pay down sleep debt and still leave you feeling sleepy at bedtime. 

We’ve covered more on the best nap length here

Head to Bed a Little Earlier Than Usual 

Try heading to bed earlier than usual to bank some more sleep. 

There’s a caveat with this piece of advice, too. If you head to bed too early, you may find it impossible to drift off. Research shows the likelihood of sleeping during the day is lowest two or three hours before your usual bedtime. This is known as the “Forbidden Zone for Sleep.” 

To avoid staring at the ceiling, check RISE for when your evening peak in energy will be. 

Expert tip: Use RISE’s smart schedule to pay back sleep debt with an earlier bedtime. Tell the app when you want to wake up and it’ll give you a goal bedtime that slowly shifts earlier to help you pay back sleep debt. RISE will also tell you how many days it’ll take you to pay back your sleep debt.

We’ve covered more advice on how to sleep early here.

Sleep in an Hour or So Later Than Usual 

Sleeping in longer than usual can help you get some more shut-eye. This can be useful at the weekend if early morning start times during the workweek have been causing sleep debt to rack up. 

Be sure to limit your lay-ins to about an hour, or two at most. Sleeping in for longer can disrupt your circadian rhythm (your body clock) and make it harder to fall asleep on time the next night. 

Expert tip: RISE’s alarm feature can help you break the habit of waking up too early and building up sleep debt. The alarm tells you, as you’re setting it, whether your chosen wake-up time will add to your sleep debt. You can then set a later time, if possible, to get more sleep and avoid piling onto your debt. 

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How long it takes to recover from sleep debt will depend on how much sleep debt you have. The more you have, the longer it will take. One study suggests one hour of sleep loss takes four days to recover from.

And there’s plenty more research backing up this theory that sleep debt can take a while to recover from. 

Dr. Jamie Zeitzer is a sleep advisor at Rise Science and the co-director of the Center for Sleep and Circadian Sciences at Stanford University. He worked on a real-world study looking at how sleep loss affects work performance. 

His paper states, “on average, it takes three nights to make up one insufficient night of sleep” and “it takes six nights to make up for two insufficient nights of sleep in a row.”

As for work performance, the study found two consecutive nights of less than six hours of sleep can decrease work performance for six days. 

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Want a solid idea of how long it’ll take you to pay back your sleep debt? RISE’s smart schedule feature will tell you how many days it’ll take to recover from your sleep debt if you follow the app’s recommended sleep times. 

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You can avoid sleep debt by making sure you get enough sleep for you each night. Once you know how much sleep you need, make it easier to get it by improving your sleep hygiene. 

Sleep hygiene is the name for the daily habits you can do to fall asleep faster, wake up less often, and get better sleep overall. 

Here’s what to do: 

• Keep a consistent sleep pattern: A regular sleep schedule will keep your circadian rhythm in check, helping you fall asleep at bedtime. We’ve got proof it works, too! RISE users with more consistent sleep-wake times have less sleep debt than those with inconsistent sleep-wake times. 
• Get bright light first thing: Morning light resets your circadian rhythm. Aim for at least 10 minutes of light as soon as possible after waking up, or 15 to 20 minutes if it's overcast or you’re getting light through a window.
• Avoid light close to bedtime: Put on blue-light blocking glasses about 90 minutes before bed (we recommend these) as light suppresses the sleep hormone melatonin. Be sure screen time before bed doesn’t cut into your sleep time. 
• Avoid caffeine, large meals, intense exercise, and alcohol too late in the day: These common sleep disruptors can keep you up past bedtime or cause you to wake up in the middle of the night, making quality sleep harder to get. RISE can tell you when to avoid each one daily to stop this from happening.  
• ‍Do a calming bedtime routine: Stress and anxiety can make it hard to get sufficient sleep. Try doing a relaxing wind-down routine an hour or so before bed to help. This could include reading, listening to music, taking a shower or bath, or doing breathing exercises. Try RISE’s in-app guided relaxation exercises, which are designed to help you drift off. 
• ‍Keep your bedroom dark, cool, and quiet: Set your thermostat to 65 to 68 degrees Fahrenheit, use blackout curtains and an eye mask, and wear earplugs or listen to white noise. 

Sleep hygiene habits are even more effective when they’re done at the right time for your circadian rhythm. RISE can tell you when to do 20+ good sleep habits each day.

RISE users on iOS 1.202 and above can click here to set up their 20+ in-app habit notifications.

Keep Track of Your Sleep Debt 

Sleep debt is the amount of sleep you’ve missed out on recently. The higher the number, the more you’re going to struggle with your energy levels, focus, well-being, and mood. And long-term sleep debt can come with serious health consequences. 

Luckily, you don’t have to work out your sleep debt by yourself. The RISE app calculates your sleep need, tracks your sleep, and automatically works out how much sleep debt you have each morning. 

RISE also guides you through 20+ sleep hygiene habits to help you get the healthy sleep you need to lower your sleep debt and keep it low. 

With RISE, you can start paying back your sleep debt fast — 80% of users get more sleep within five days.