Sleep debt is the running total of the difference between the sleep you need and the sleep you actually get. Fall an hour short each night and the deficit accumulates across the week.

Can you catch up on lost sleep?

Partly. Extra sleep over a few nights can repay recent, modest debt, but research shows it doesn't fully reverse the effects of chronic short sleep. Consistency beats occasional recovery.

How much sleep debt is too much?

There's no hard threshold, but the larger and more chronic the debt, the more it impairs mood, focus and recovery. Around 5 hours or more of weekly debt is worth acting on; 10+ hours is significant.

How long does it take to recover from sleep debt?

Small debts can clear in a few nights of adequate sleep. Larger or long-standing debts can take a week or more of consistent, sufficient sleep — not one marathon lie-in — to recover from.

Does sleeping in on weekends fix sleep debt?

Weekend catch-up sleep helps a little but rarely repays a full week's deficit, and big swings in your schedule can disrupt your body clock. Steady, sufficient sleep every night works better.

Sleep Debt Calculator

This sleep debt calculator adds up how far your sleep fell short of your nightly need over the past week, so you can see your accumulated shortfall — and your average night — in one place.

How it works

Set how many hours of sleep you need each night, then enter how long you actually slept on each of the last seven nights. For every night the calculator works out the gap between your need and your sleep, then adds those gaps together:

Sleep debt = the sum of (nightly need − hours slept) across every night you logged.
A positive total means you under-slept and owe sleep; a negative total is a surplus.
Leave a night blank to skip it — only the nights you fill in are counted, and your average reflects just those nights.

Worked example

Suppose you need 8 hours a night and over a week you slept 6, 7, 6, 8, 5, 7 and 6 hours. The nightly shortfalls are 2 + 1 + 2 + 0 + 3 + 1 + 2 = 11 hours of sleep debt, while your average night was 6.4 hours. That's a moderate debt: the fix is a few consistent nights of fuller sleep, not a single long lie-in.

Reading your sleep debt

A rough guide to weekly sleep debt and what to do about it:

Weekly debt	Level	What it suggests
0 h or less	On track	You're meeting (or beating) your sleep need.
1–5 h	Mild	Easily repaid with a couple of fuller nights.
5–10 h	Moderate	Prioritise earlier nights for several days.
10 h or more	Significant	Rebuild with consistent extra sleep, not one long lie-in.

A guide only — individual sleep needs and tolerance for debt vary.

Plan your recovery

To work out the bedtimes that meet your nightly need, use the Sleep Calculator. A well-timed nap can blunt the effects of a bad night, and your recovery score helps you see how sleep debt is affecting your readiness to train.

Frequently asked questions

What is sleep debt?: Sleep debt is the running total of the difference between the sleep you need and the sleep you actually get. Fall an hour short each night and the deficit accumulates across the week.
Can you catch up on lost sleep?: Partly. Extra sleep over a few nights can repay recent, modest debt, but research shows it doesn't fully reverse the effects of chronic short sleep. Consistency beats occasional recovery.
How much sleep debt is too much?: There's no hard threshold, but the larger and more chronic the debt, the more it impairs mood, focus and recovery. Around 5 hours or more of weekly debt is worth acting on; 10+ hours is significant.
How long does it take to recover from sleep debt?: Small debts can clear in a few nights of adequate sleep. Larger or long-standing debts can take a week or more of consistent, sufficient sleep — not one marathon lie-in — to recover from.
Does sleeping in on weekends fix sleep debt?: Weekend catch-up sleep helps a little but rarely repays a full week's deficit, and big swings in your schedule can disrupt your body clock. Steady, sufficient sleep every night works better.

Related calculators

Disclaimer. This calculator offers general guidance and is not medical advice. Persistent sleep problems, daytime sleepiness, or suspected sleep disorders warrant a conversation with a doctor.