Sleep Debt Calculator
Add up a week of short nights and see what it actually costs.
Hours slept each night
Your debt
Debt accumulates faster than it clears
Sleep debt is the running total of the gap between what you need and what you get. An hour short on five weeknights is a five-hour debt by Friday, and the effects compound rather than staying level — after a week of restriction, performance on attention tasks degrades to a degree comparable with having gone a full night without sleep.
The uncomfortable part is that you stop noticing. Subjective sleepiness plateaus after a few nights of restriction while objective performance keeps falling, so people who are substantially impaired frequently report feeling fine. That gap between how you feel and how you perform is the genuinely dangerous feature of chronic partial sleep loss.
Recovery is possible but asymmetric. A single long weekend lie-in repays some of the deficit and not all of it, and research suggests some markers of impairment persist after apparently adequate recovery sleep. Spreading recovery across several nights of an extra hour works better than one very long night, and shifting weekend sleep dramatically later brings its own problem — social jetlag, where the body clock moves and Monday morning becomes harder still.
Medical disclaimer. This calculator is for general information and education only. It is not medical advice, not a diagnosis, and not a substitute for professional care. Persistent daytime sleepiness despite adequate time in bed can indicate sleep apnoea or another sleep disorder, which is worth investigating rather than managing with recovery sleep.Speak to a doctor or another qualified clinician about any health decision.Last reviewed .
Frequently asked questions
Can you catch up on lost sleep?
Partially. Recovery sleep repays much of the deficit, but some studies find markers of impairment persisting even after apparently adequate recovery. Spreading it across several nights of an extra hour works better than a single very long lie-in.
How much sleep do adults actually need?
Most adults need 7-9 hours, with genuine individual variation inside that range. People who function well on substantially less are far rarer than the number who believe they are — the feeling of adapting is usually the perception plateau rather than real adaptation.
Why do I feel fine despite being short on sleep?
Because subjective sleepiness plateaus after a few nights of restriction while objective performance continues to decline. You stop feeling worse while continuing to get worse, which is the most dangerous feature of chronic partial sleep loss.
Is sleeping in at weekends a good idea?
It repays some debt, but shifting sleep timing by several hours creates social jetlag — the body clock moves and Monday becomes harder. Keeping wake times within about an hour across the week is generally better than a large weekend swing.
What does sleep debt actually do?
Attention, reaction time, working memory and emotional regulation all degrade measurably. Longer term it is associated with impaired glucose tolerance, raised blood pressure and reduced immune function.