Sleep debt is simply the gap between the sleep you need and the sleep you got, added up across nights. This tool does that arithmetic on the numbers you type, against a target you choose. That is all it does — it is not a measurement of your body, and it cannot diagnose anything.

General wellness information, not medical advice; no doctor–patient relationship is formed. This is arithmetic on self-reported numbers. It does not diagnose or screen for insomnia, sleep apnoea, narcolepsy, or any circadian rhythm disorder. Persistent difficulty sleeping, loud snoring or breathing pauses, or severe daytime sleepiness deserve a clinician, not a calculator.

Your last seven nights

The AASM and Sleep Research Society recommend adults sleep 7 or more hours per night on a regular basis. Individual need genuinely varies, and there is no validated formula that turns your age or weight into a personal number — so you set the target, and we label it a guideline rather than a diagnosis.

What that number is — and what it is not

It is a bookkeeping figure: hours below the target you chose, over the nights you entered. It is not a quantity sitting in your body waiting to be repaid, and this page will not give you a repayment schedule, because the evidence does not support one.

  • Recovery is not one-for-one. After five nights restricted to four hours, a single ten-hour recovery night left recovery incomplete — the rebound is uneven and tapers rather than settling a balance (Banks et al., 2010).
  • Weekend catch-up is not a reset. In a controlled study, weekend recovery sleep did not prevent the metabolic dysregulation caused by recurrent insufficient sleep (Depner et al., 2019).
  • The popular “four days per lost hour” figure is thin. It comes from one small laboratory study whose participants were all men (Kitamura et al., 2016). We mention it only so you can recognise it; we do not compute a personal countdown from it. The frequently repeated “nine days to clear your sleep debt” claim has no traceable primary source at all.

Why it still matters that it adds up

The deficit is real even though the repayment metaphor is not. In a landmark study, fourteen consecutive nights restricted to six hours or less produced cumulative, dose-dependent cognitive deficits — performance comparable to up to two nights of total sleep deprivation. The finding worth sitting with is this one: participants were largely unaware of how impaired they had become (Van Dongen et al., 2003). Self-rated sleepiness is a poor gauge, which is exactly why writing the hours down is worth doing.

Habitually short sleep is associated with increased risk for obesity, diabetes, high blood pressure, coronary heart disease, stroke, frequent mental distress, and all-cause mortality (CDC/MMWR). Association is not causation, and no calculator can tell you your personal risk.

Why seven nights

Seven nights is the smallest window that survives one unusual night, and it is a user-interface convention rather than a validated physiological period. The research window that produced the clearest cumulative effects was fourteen nights. Treat the total as a description of the week you entered, nothing wider.

Nothing here leaves your browser

The arithmetic runs in JavaScript on your own device. No sleep hours are transmitted, none are written to storage, and nothing is attached to an email address. Sleep data tied to an identity is exactly the sort of thing that should not accumulate on a marketing site.

If you want to see it over more than a week

Counting a week by hand is useful once. Watching whether short nights actually track with how you feel is the harder question, and it is what HealthMaxxing is built for — sleep sits on the same timeline as mood, food, and movement, and the open protocol treats “no clear relationship” as a valid answer. It is coming soon. You can also read sleepmaxxing done right.

  1. Watson NF, et al. “Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the AASM and Sleep Research Society.” — J Clin Sleep Med. 2015;11(6):591-2. Source of the 7-or-more-hours guideline.
  2. Van Dongen HPA, et al. “The cumulative cost of additional wakefulness.” — Sleep. 2003;26(2):117-126. Cumulative dose-dependent deficits, and the unawareness finding.
  3. Banks S, et al. “Neurobehavioral dynamics following chronic sleep restriction: dose-response effects of one night for recovery.” — Sleep. 2010;33(8):1013-26. Recovery is incomplete after a single extended night.
  4. Depner CM, et al. “Ad libitum weekend recovery sleep fails to prevent metabolic dysregulation…” — Current Biology. 2019;29(6):957-967. Weekend catch-up is not a reset.
  5. Kitamura S, et al. “Estimating individual optimal sleep duration and potential sleep debt.” — Sci Rep. 2016;6:35812. Origin of the “four days per hour” figure; small, male-only sample.
  6. CDC/MMWR: “Prevalence of Healthy Sleep Duration among Adults — United States, 2014.” — Source of the “associated with” risk language.

Evidence reviewed July 24, 2026 · Corrections: hello@maxxing.health