Sleep Debt Calculator

How the debt is calculated

The weekly debt is your target times seven, minus the seven nights you entered, floored at zero — so a 8-hour target against 49 hours slept is a 7-hour debt, and sleeping more than your target does not earn credit. The 30-, 90- and 365-day projections take your average nightly shortfall and repeat it: 45 minutes short a night is 22.5 hours over a month and 274 over a year. That is straight multiplication, which is what makes it a projection of the pattern rather than a measurement of your body.

Two of the numbers on this page are ours and neither has a citation behind it. The cognitive performance figure subtracts 13 percentage points for every hour of average nightly shortfall and stops at 30 per cent — so an hour short reads 87 per cent, two hours 74. That slope is our own construction. The research it gestures at is real and much less tidy: restricting sleep across consecutive nights produces cumulative deficits on attention tasks, and people rate themselves as barely impaired while measuring as substantially impaired. A single percentage of general performance is not something that literature supports, and we would rather say that than pretend the number is a finding.

The recovery estimate is the same kind of figure. It divides your debt by the hours a 9-hour night gives you above your own target, so an 8-hour target recovers one hour a night and a 7-hour target two. Real recovery is not linear like that — the first long night returns more than the fifth — and 9 hours is an assumption we picked as a plausible catch-up night. Read the number as an order of magnitude for how long the hole takes to fill, not as a schedule.

The studies the page's prose leans on are the three below: the 14-night restriction experiment that found cumulative deficits and volunteers who did not notice them, the sleep-extension study in which an hour of nightly debt took about four nights to clear, and the National Sleep Foundation panel behind the 7-to-9-hour range. None of them produced the percentage or the recovery figure above; those are ours.

Where these numbers come from

1. 1. The cumulative cost of additional wakefulness: dose-response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation — Van Dongen HP, Maislin G, Mullington JM, Dinges DF, Sleep 26(2):117–126, 2003 (PubMed)
2. 2. Estimating individual optimal sleep duration and potential sleep debt — Kitamura S et al., Scientific Reports 6:35812, 2016 (PMC)
3. 3. National Sleep Foundation's sleep time duration recommendations: methodology and results summary — Hirshkowitz M et al., Sleep Health 1(1):40–43, 2015 (PubMed)

Nothing on this site is medically reviewed. Every figure above was read out of the code that runs on this page, and where a number is our own judgement rather than a published one, the note says so and cites nothing. Method last checked 25 September 2026.