Sleep Debt Calculator
Log your last 7 nights. The tool compares each night to your age group's recommended sleep and shows your running total — how many hours of sleep you owe your body this week.
What "sleep debt" actually means
Sleep debt is the running gap between the sleep your body needs and what you actually get. Miss 90 minutes a night, five nights in a row, and you're carrying 7.5 hours of debt — roughly a full night. The Van Dongen study found that two weeks of 6-hour nights caused cognitive impairment on par with two nights of no sleep, even though participants said they felt "fine."
Weekend catch-up helps with alertness but doesn't fully restore metabolism or hormone regulation. The realistic protocol is 3–7 nights of adding 60–90 minutes to your normal window, not one heroic 12-hour Saturday.
What sleep debt actually is
Sleep debt is the running gap between the sleep your age group needs and the sleep you actually got. It is a useful arithmetic, but it is not a bank balance. Sleep loss accumulates in the sense that performance keeps degrading across consecutive short nights — the classic dose-response studies on restricted sleep show cognitive decline continuing to build night after night, while people’s sense of how impaired they are plateaus after a few days. That mismatch is the real hazard: you adapt to feeling tired long before you adapt to being tired.
You cannot repay it hour for hour
If the calculator says you are twelve hours down, sleeping twelve extra hours on Saturday will not undo it. Recovery sleep is denser rather than longer: the first recovery nights show rebound in deep slow-wave sleep, with REM catching up over subsequent nights. A single long lie-in restores some alertness and also pushes your body clock later, which is how people manufacture a difficult Sunday night and a brutal Monday. The workable pattern is boring — add sixty to ninety minutes a night across four or five nights, and keep the wake time anchored while you do it.
Reading your result honestly
- Under 5 hours of debt — normal week-to-week variation. Protect your wake time and it clears on its own.
- 5–10 hours — the range where reaction time and mood are measurably worse even though you feel functional. Add an hour a night for a week.
- Over 10 hours — treat this as a schedule problem, not a willpower problem. Something structural — shift pattern, commute, second job, a baby — is setting the ceiling, and no evening habit change will out-run it.
Two caveats worth stating plainly. First, the target here is age-adjusted guidance, not a personal prescription; individual need genuinely varies by roughly an hour either side, and a small minority sit outside that. Second, the hours you enter are time in bed as you remember it, which for most people over-states real sleep by half an hour or so. If your debt looks alarming, check whether you are counting time awake in bed as sleep.
When the number is not the problem
If you are spending eight hours in bed and still waking unrefreshed, this calculator is measuring the wrong thing. Persistent unrefreshing sleep at adequate duration points at quality or a disorder — fragmented sleep, untreated sleep apnoea, restless legs, or a circadian mismatch between your body clock and your alarm — and those need assessment rather than more hours. Loud snoring with witnessed pauses in breathing, or falling asleep involuntarily during the day, are reasons to see a doctor rather than to recalculate.
Nothing you enter leaves your device: the seven nights and your age group are held in your browser only.