The accumulated difference between the sleep you needed and the sleep you got. Missing an hour a night for a week is a seven hour debt, and it does not disappear on its own.

Can you catch up on sleep at the weekend?

Partly, but not completely, and a long lie-in shifts your body clock later so Sunday night becomes hard. Adding an extra hour across several nights works better than one long morning.

How long does it take to recover from sleep debt?

Roughly an extra hour a night, so about a week to clear a seven hour debt. Larger debts built over months take considerably longer.

How much sleep do adults need?

Most adults need seven to nine hours. The practical test is whether you wake without an alarm feeling rested, rather than any specific number.

Sleep debt calculator

Enter the last seven nights. See what you are actually carrying.

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Your nightly target

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Most adults need 7 to 9. Use the figure where you wake without an alarm.

Hours actually slept

Last night

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2 nights ago

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3 nights ago

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4 nights ago

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5 nights ago

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6 nights ago

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7 nights ago

hrs

Time asleep, not time in bed. Most people overestimate by about 30 minutes.

Sleep debt

7 hr 30 min

Across 7 nights

Average night: 6 hr 56 min
Shortest night: 6 hr
Total slept: 48 hr 30 min
Nights to repay: 8

Repay it across several nights rather than one long weekend. A lie-in until noon shifts your body clock later, which makes Sunday night hard and starts the next week already behind.

An alarm clock beside a bed in dim morning light

Debt accumulates faster than it repays

Missing 90 minutes a night across a working week is a debt of seven and a half hours by Friday. People then plan to clear it with one long Saturday, which does not work, because you cannot sleep 15 hours in one go and you would wreck the following night if you did.

Recovery runs at roughly an extra hour a night. So a seven hour debt takes about a week of slightly longer nights, which is a far less satisfying answer than a lie-in and a far more accurate one.

What the debt actually costs

The measurable effects show up in reaction time, working memory, and mood well before you feel tired, which is the dangerous part. People carrying a substantial debt routinely rate their own alertness as fine.

This is worth naming plainly: the subjective sense of having adapted to short sleep is not evidence of having adapted to it.

The weekend lie-in problem

Sleeping until noon on Saturday shifts your body clock later, and Sunday night then becomes hard, which starts the next week already behind. The pattern has a name, social jetlag, and it is why some people feel worse on Monday after more total sleep.

A better approach is going to bed 30 to 60 minutes earlier for several nights and keeping the wake time roughly fixed. It is duller and it works.

How to calculate your sleep debt

1
Set your target
Seven to nine hours suits most adults. Pick the figure where you feel fine without an alarm.
2
Enter the last seven nights
Actual sleep, not time in bed. Most people overestimate by around 30 minutes.
3
Read the total
The shortfall accumulates. A nightly gap that feels trivial is several hours across a week.
4
Plan the repayment
About an extra hour a night, not one enormous weekend. Keep your wake time steady.

Questions people ask

What is sleep debt?: The accumulated difference between the sleep you needed and the sleep you got. Missing an hour a night for a week is a seven hour debt, and it does not disappear on its own.
Can you catch up on sleep at the weekend?: Partly, but not completely, and a long lie-in shifts your body clock later so Sunday night becomes hard. Adding an extra hour across several nights works better than one long morning.
How long does it take to recover from sleep debt?: Roughly an extra hour a night, so about a week to clear a seven hour debt. Larger debts built over months take considerably longer.
How much sleep do adults need?: Most adults need seven to nine hours. The practical test is whether you wake without an alarm feeling rested, rather than any specific number.