Add up your sleep debt over the last 7 nights, see your average sleep, and get a simple payback plan. Free, no signup, runs on your device.
Most adults need 7–9 hours. 8 is a sensible default.
Add +1.5 h of sleep for 6 nights to clear it. Earlier bedtimes beat sleeping in — they keep your wake time stable.
Sleep debt is the cumulative difference between the sleep you need and the sleep you get. The concept is straightforward arithmetic: if your body needs 8 hours and you sleep 6.5, you fall 1.5 hours short — and that shortfall carries over to the next day. Do that for a working week and you can be carrying 7–10 hours of accumulated debt by the weekend, even though no single night felt disastrous. According to the Sleep Foundation, that debt has real costs: slower reaction time, worse mood, weaker concentration, and impaired immune and metabolic function.
This calculator uses the standard formula — debt = Σ max(0, target − actual) over your last seven nights. Surplus nights, where you sleep more than your target, are deliberately not allowed to cancel out deficit nights, because the evidence is that you can owe sleep far more reliably than you can bank it ahead of time. Most adults need 7–9 hours; the default target of 8 is a reasonable middle, but set it to your own number.
The good news is that short-term debt is recoverable. The catch is that one giant weekend lie-in doesn't do it cleanly — it can shift your body clock later and leave you groggy. A better plan is to add a modest, consistent amount of sleep over several nights. This tool caps recovery advice at an extra 1.5 hours per night and shows you how many nights of that it takes to clear your balance. Going to bed earlier tends to beat sleeping in, because it protects a stable wake time.
The single biggest lever against chronic sleep debt is a consistent bedtime — the deficit never accumulates if you hit your target most nights. That's a textbook habit: same cue (a wind-down alarm), same action (lights out), tracked daily. You can set a "lights out by 11pm" habit in HabitBox and log a one-tap check-in each night — free, no account, on-device, on iOS and Android — and watch the streak hold your bedtime steady so the debt simply stops building.
Note: this is a general estimate for healthy adults. Persistent fatigue despite adequate time in bed, loud snoring, or non-restorative sleep can signal a sleep disorder such as insomnia or sleep apnea — worth raising with a clinician.
Sleep debt is the running total of sleep you've missed relative to what your body needs. If you need 8 hours but average 6.5, you accumulate about 1.5 hours of debt each night — roughly 10.5 hours across a week. The deficit builds up and impairs attention, mood, and reaction time even when you feel 'used to it'.
This tool sums each night's shortfall against your target: debt = Σ max(0, target − actual) across the last 7 nights. Nights where you slept more than your target don't subtract from the debt, because banking extra sleep ahead of a deficit doesn't reliably work the way owing sleep does.
Short-term debt is recoverable. Research summarised by the Sleep Foundation suggests it can take several days of consistent, slightly longer sleep to recover from a week of moderate loss — not a single long lie-in. Chronic, long-term restriction is harder to reverse and is linked to metabolic and cardiovascular risk.
Aim for an extra 1–1.5 hours per night rather than one marathon sleep. This calculator plans your payback at +1.5 hours/night and tells you how many nights that takes. Going to bed a little earlier is usually more effective and sustainable than sleeping in, which can push your body clock later.
Partly, but imperfectly. Studies cited by the Sleep Foundation show weekend recovery sleep can reverse some short-term effects, but it doesn't fully restore metabolic markers and can disrupt your circadian rhythm — making Monday harder. A consistent schedule beats a weekday-deficit, weekend-binge cycle.
The surest way to clear sleep debt is to stop it building. HabitBox lets you set a 'lights out by 11pm' habit, tap once to log it each night, and keep a streak that holds your schedule steady — free, no account, on-device.
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