What Is Sleep Debt and Can You Catch Up on Lost Sleep?

We’ve been making mattresses here in the UK for over 25 years, and we get questions about tiredness on our phones and in John Ryan’s inbox almost every day. So we’ve pulled together what the sleep research says about sleep debt, whether you can pay it back, and the honest bit about when your bed is part of the problem or when it’s just poor sleeping habits or burning the candle at both ends.

The short answer is that you can claw back some lost sleep, but one long lie-in won’t wipe the slate clean. Here’s what’s going on and what we’d do about it.

In this guide:

• What is sleep debt?
• How much sleep do you actually need?
• How to work out your own sleep debt (with our calculator)
• Signs you’re running a sleep debt
• Can you catch up on lost sleep?
• How long does it take to recover?
• How to pay back sleep debt
• When your mattress is adding to the debt
• When it isn’t sleep debt
• Sleep debt FAQs

What is sleep debt?

Sleep debt (also called a sleep deficit) is the running total of sleep you’ve missed compared with what your body needs. Miss an hour tonight, and you’re an hour down. Miss an hour every night for a workweek, and you’re five hours down by Friday, more than half a night’s sleep.

Sleep scientists tend to split it into two kinds. Short-term debt is the odd late night: a party, a poorly child, an early flight. Chronic sleep debt is the slow, grinding kind, where you’re short by 30 to 90 minutes most nights for months or even years, until feeling tired just becomes your normal.

It’s the chronic kind we worry about, because once you stop noticing, it’s gone. We’ll come back to why that’s a problem in a moment.

We’ve been there ourselves

I know how brutal sleep debt can be, because it hit John and me hard when we started running the UK’s first online bed retailer, working with our suppliers on handmade natural fibre mattresses, then delivering them ourselves.

Every week was a juggling act. John drove the van while I was on my old BlackBerry, taking calls, answering emails, and advising sleepers, all while we were out delivering beds.

For the first few years, any holidays involved a whole lot of sleep. It wasn’t sustainable, and luckily the business grew enough for us to take on staff, but we both know firsthand what proper sleep debt feels like.

A quick example

Say you need eight hours and you’ve been getting six and a half on work nights. That’s 90 minutes a night, 7.5 hours over five nights.

By Friday evening, you’re carrying almost a full night’s sleep you never had. No wonder the sofa looks so inviting after tea!

How much sleep do you actually need?

The NHS says most adults need between seven and nine hours a night. That’s a fairly wide range, and where you sit within it depends as much on your genes as your habits.

A good way to find your own number is to watch what happens in the second week of a holiday: once you’ve paid off the backlog, you’re going to bed at a sensible time, with no alcohol, and you naturally settle. What you get is roughly what your body is asking for.

When people tell us they “only need six hours”, we’d gently suggest they test that theory on holiday first. A few true short sleepers do exist, but they’re rare, and most of us are simply used to being tired.

It’s also about the quality of those hours. Your body cycles through light, deep, and REM sleep several times a night, and if you wake often, you lose chunks of the deeper stages. We’ve covered this in our guide to how much of each sleep phase you need.

How to work out your own sleep debt

You don’t need an app for this, though a sleep tracker helps if you already have one. A pen and the back of an envelope will do.

For one week, jot down roughly what time you fell asleep and what time you woke up. Don’t count the time spent scrolling in bed, because that isn’t sleep (sorry). Then take each night away from your target and add up the shortfall.

Here’s what a fairly typical week looks like for someone who needs eight hours:

In that example, the Saturday lie-in pays back one hour; you’re still owed five and a half hours going into Monday. That’s the trap most of us fall into: the weekend feels restful, yet the balance never quite clears.

Try our sleep debt calculator

If you’d rather we did the maths for you, pop your own week into the calculator below. Pick how much sleep you think you need, then roughly how long you slept each night, and it’ll tell you what you owe and how quickly an earlier bedtime would clear it.

Signs you’re running a sleep debt

The obvious sign is feeling tired, but sleep debt is sneakier than that. These are the things we’d look out for in yourself:

• Nodding off within minutes of sitting down in the evening
• Needing an alarm and the snooze button every single morning
• Relying on coffee or energy drinks to get through the afternoon
• Forgetfulness, poor concentration or a short fuse
• Craving sugary snacks, especially later in the day
• Sleeping far longer at weekends than on work nights

Why you can’t always tell

Here’s the bit that surprised us. In a well-known 2003 study from the University of Pennsylvania (Van Dongen and colleagues, published in the journal Sleep), researchers kept participants in bed for only 6 hours a night for two weeks.

By the end, their reaction times and concentration had dropped to the level of people kept awake for up to two nights straight. Yet when asked, they said they felt only a little sleepy.

So the longer you carry a sleep debt, the worse you get at judging how tired you really are.

That’s a real worry on the roads. RoSPA estimates that driver fatigue may be a factor in up to one in five accidents on major roads, so if you’re yawning behind the wheel, pull over somewhere safe and take a proper break.

Can you catch up on lost sleep?

Well, yes and no. If you’ve had one or two rough nights, a couple of early nights will put you more or less back where you started. You recover from short-term debt partly by getting more deep sleep the following night.

Chronic debt is a different story. Researchers in Japan (Kitamura and colleagues, Scientific Reports, 2016) let healthy young men sleep for as long as they liked, night after night. It took days for their sleep to return to its natural length, and the team estimated that around four days of unrestricted sleep were needed to recover from just one hour of sleep debt.

Four days for one hour. If you’re carrying five or six hours of sleep debt from a workweek, a single Saturday lie-in barely touches it.

What about weekend lie-ins?

We’d love to tell you the weekend lie-in fixes everything. Sadly, the research is mixed.

A 2019 study from the University of Colorado Boulder (Depner and colleagues, Current Biology) kept volunteers to five hours a night during the week, then let one group sleep in at the weekend. The weekend sleepers didn’t escape the downsides. They still snacked more after dinner, and their bodies handled sugar less well than when they’d been sleeping properly. In contrast, a large Swedish study (Åkerstedt and colleagues, Journal of Sleep Research, 2018) followed more than 43,000 adults for 13 years. Among those under 65, people who slept short during the week but longer on weekends didn’t show the higher death rate seen in people who slept short all week, so that extra weekend sleep seems to do some good.

Our take on all of this? Treat the weekend lie-in as a handy top-up, and keep your real repayment plan for weeknights. Getting enough sleep most nights of the week is the way to clear chronic sleep debt for good.

How long does it take to recover from sleep debt?

There’s no exact formula, because everyone’s sleep needs are different. One bad night usually sorts itself out within a night or two, especially if you go to bed a little earlier and let your body get the deep sleep it needs.

A week of short nights might take a week or so of proper sleep before you feel sharp again. Chronic debt built up over months can take several weeks of steady, sensible sleep to pay off, and you’ll probably notice your mood and concentration improve before the tiredness fully lifts.

The good news is that you don’t have to pay it back hour for hour. Nobody needs to sleep 14 hours to cancel 14 hours of debt (and if you try, you’ll wake up feeling like you’ve been hit by a bus). Your body wants consistency.

How to pay back sleep debt without wrecking your body clock

This is the approach we’d suggest. None of it is complicated, but it does take a few weeks and a bit of discipline.

Move your bedtime earlier by 15 to 30 minutes

Your wake-up time anchors your body clock, so keep it roughly the same every day and claw back sleep at the other end by going to bed 15 to 30 minutes earlier. Once that feels normal, try another 15 minutes.

It sounds too small to matter. Over a week, though, an extra half hour a night pays back three and a half hours of debt, with no grogginess and no Monday morning hangover.

Keep weekend lie-ins to an hour or two

Sleeping until noon on Sunday shifts your body clock, which is why Sunday night can feel impossible and Monday morning so grim. Sleep scientists call this social jet lag.

An extra hour or two is plenty. If you’re still exhausted, go to bed early instead. Our guide to circadian rhythms and sleep quality explains why your body clock is so fussy.

Use naps carefully

A short nap can ease the afternoon slump. In NASA’s well-known study of long-haul pilots, crews who took a planned nap (averaging about 26 minutes asleep) performed 34% better and were 54% more alert than those who didn’t, which isn’t bad for a kip in the cockpit.

We’d keep naps to 10 to 30 minutes and finish by mid-afternoon, or you’ll struggle to fall asleep at bedtime. Our guide to power napping goes into more detail.

Protect the hour before bed

Caffeine hangs around in your system for hours, so we’d stop coffee and strong tea by early afternoon. If you can, charge your phone outside the bedroom, and keep your room cool, dark, and quiet.

We’ve covered more of these habits in our sleep hygiene guide and our tips to stop smartphone sleep sabotage.

Get up if you can’t sleep

If you’ve been lying awake for what feels like 20 minutes, get up, go to another dimly lit room and do something boring until you feel sleepy. Lying there and watching the clock teaches your brain that bed is a place to worry.

When your mattress is adding to the debt

This is where mattress-makers make their money: many people spend eight hours in bed and wake up shattered because they’re getting six hours of decent sleep out of those eight.

The hotel sleep effect

People call us all the time saying they want that hotel sleep. Part of it may well be the mattress, but people forget that a hotel stay usually means a holiday, where you can sleep longer and properly switch off.

So without realising it, you’re paying off your sleep debt! It’s worth asking yourself whether you loved the hotel or the extra hours you spent there.

That said, your mattress can chip away at your sleep in three main ways. It can leave you too hot, it can pass your partner’s every move across to you, or it can be the wrong spring tension for your weight, so you toss and turn all night looking for a comfortable spot.

If any of those sound familiar, our guide on why you might still be tired after 8 hours of sleep is worth a read.

Running hot

Memory Foam and thick polyester layers trap your body heat, and many sleepers wake more often. Natural fibres such as Wool, Cotton and Mohair let heat and moisture move away from your body, which is exactly why we fill our mattresses with them.

See why natural fibres suit hot sleepers.

A restless partner

Every time your other half turns over, a conventional mattress passes the motion to your side. Individually pocketed springs move independently, so you feel far less of it.

For couples with very different weights or sleep habits, a zip-and-link mattress lets each side have its own spring tension. Our guide on how to stop your partner waking you up covers the rest.

The wrong spring tension

Pick the wrong spring tension and no amount of Wool on top will fix it. Too soft and you sink; too firm and your hips and shoulders take a pounding.

Either way, you’ll be shuffling about half the night, the kind of broken sleep that builds a debt. We’ve written more on choosing the best mattress if you toss and turn all night.

What we’d recommend (king size prices)

If your current mattress is past its best, these are the two we’d point most tired customers towards. Prices are for a king size, our reference size.

Origins Pocket 1500, £1,050 king size. This has 1,500 spun-bond pocket springs under 300gsm of Wool, with 1,550gsm of upholstery and a one-inch Foam insulator layer.

It’s two-sided, so you can turn it and get far more years out of it. If your budget is tight, this is the one we’d buy.

Artisan Naturals, £2,180 king size. This one has 1,600 calico encased pocket springs (1.28mm gauge) under 1,200gsm of blended British fleece Wool and Cotton, 1,250gsm of rebound poly Cotton and 1,500gsm of pure Mohair, 3,950gsm in all.

Hand-side-stitched and two-sided, and for a hot sleeper, it’s where we’d spend our own money.

Both come with our 60-day Love It or Return It guarantee, but the more useful thing is a quick chat with us. Please tell us your weight, how you sleep, and whether you run hot, and we’ll tell you which tension to go for, even if that means a cheaper mattress than you expected.

When it isn’t sleep debt

If you’re getting seven to nine hours most nights, your bed is comfortable, and you’re still exhausted, something else may be going on. Loud snoring with pauses or gasps can signal sleep apnoea, and struggling to fall asleep or stay asleep for three months or more is worth mentioning to your GP.

Ongoing tiredness can also be linked to things like an underactive thyroid or anaemia, so don’t just put it down to a busy life. Our guide to common sleep disorders is a good starting point, and your GP can check the rest.

If you work nights or rotating shifts, sleep debt works a little differently because you’re sleeping against your body clock. Our shift work sleep guide covers that in detail.

Sleep debt FAQs

What is sleep debt in simple terms?

Sleep debt is the difference between the sleep your body needs and the sleep you actually get, added up over several nights. If you need eight hours and get six and a half for five nights, you’ll owe around seven and a half hours by Friday.

Is sleep debt real?

Yes. Studies show that regularly sleeping less than you need affects your reaction time, concentration, mood and appetite, and the effects build up night after night. People carrying chronic sleep debt often underestimate how tired they are.

Can you catch up on sleep at the weekend?

Partly. A weekend lie-in pays back some of the debt, but research suggests it doesn’t undo all the effects of short sleep during the week. Keep lie-ins to an extra hour or two and focus on getting enough sleep on weeknights.

How long does it take to catch up on lost sleep?

One or two bad nights usually take a night or two to recover from. Longer-term debt takes much longer: one study estimated that recovering from a single hour of sleep debt took around four days of unrestricted sleep.

Can you catch up on sleep by napping?

A 10 to 30 minute nap can ease daytime sleepiness and pay back a little of the debt. Finish naps by mid-afternoon, though, because long or late naps make it harder to fall asleep at night and keep the cycle going.

How do you calculate sleep debt?

Decide how many hours you need (most adults need seven to nine), then note how long you sleep each night for a week. Take each night away from your target and add up the shortfalls to get your weekly sleep debt.

How much sleep do adults need?

The NHS says most adults need between seven and nine hours of sleep a night. Your own need depends on you, so pay attention to how much you naturally sleep on holiday once you’re well rested.

Is it bad to have a long lie-in to catch up?

A long lie-in shifts your body clock, so you’ll find it harder to fall asleep that night and harder to get up the next morning. An extra hour or two is fine; beyond that, go to bed earlier instead.

Why do I sleep better in a hotel?

Sometimes it’s the mattress, but a hotel stay usually means a holiday, where you sleep longer and properly switch off. Without realising it, you’re paying back your sleep debt, which is a big part of why you wake up feeling so much better.

Can a better mattress help with sleep debt?

It can if your mattress is what’s waking you. A bed that’s too hot, too soft, too firm, or that passes on your partner’s movement cuts into your sleep, and fixing that helps you bank more sleep every night.

Our final word on sleep debt

Sleep debt is real; it builds up faster than most of us realise, and you can’t clear months of it with one Saturday lie-in. What works is fairly unexciting: a steady wake-up time, a slightly earlier bedtime, the odd short nap and a bedroom (and a bed) that lets you stay asleep once you get there.

If you think your mattress might be part of the problem, give our small team a ring on 0161 437 4419 or drop us a message below. We’ll ask a few questions about how you sleep and give you a straight answer, even if it’s that your mattress is fine and you just need an earlier night.