What is sleep debt?

Every night you sleep less than your body needs, the shortfall adds up. Miss an hour for five nights and you carry a five-hour sleep debt into the weekend. Research shows this debt is real: the effects of short sleep accumulate, steadily eroding attention, reaction time, mood and decision-making — often without you noticing how impaired you have become.

This calculator adds up the gap between your target and your actual sleep across seven nights to show the total you owe.

How it is calculated

The maths is simple: your weekly target is your nightly goal multiplied by seven. Your sleep debt is that target minus the total hours you actually slept. For example, with an 8-hour target (56 hours a week), sleeping a total of 49 hours leaves a 7-hour debt.

The tool also shows your average nightly sleep and how many nights fell short, so you can see whether the problem is the occasional bad night or a consistent weekday shortfall.

How to repay sleep debt

Small, recent sleep debt can be recovered within a few days. The best approach is gradual: add an extra hour or two per night rather than attempting one enormous weekend lie-in, which can throw off your body clock and make Monday harder. Going to bed earlier is usually better than sleeping in late.

Chronic, long-term sleep debt is harder to undo and is linked to higher risks of weight gain, heart disease and impaired immunity. The most reliable fix is prevention: a consistent schedule, a dark and cool bedroom, and limiting caffeine and screens before bed. If you regularly cannot get enough sleep despite trying, speak to a healthcare professional.

Frequently asked questions

Sources & references