How the sleep debt calculator works
How debt accrues
Every night below your personal need deposits a deficit hour (or three). The body keeps partial score: reaction time, mood, and glucose metabolism degrade measurably by 3–4 cumulative hours, and two weeks of 6-hour nights perform like one totally sleepless night in vigilance testing — while feeling almost fine. The subjectively quiet accumulation is what makes debt dangerous.
How repayment actually works
Recovery sleep is real: the brain prioritizes deep and REM stages, and one or two longer mornings restore most function. The efficient protocol: +45–90 minutes nightly for a week, or two weekend mornings +2 hours (keeping wake time within ~2 hours of usual to protect the rhythm). All-or-nothing Sunday marathons repay less than they cost in rhythm disruption.
The need input is personal
"7–9 hours" is a population band; individuals sit stably at 6.5 or 9.5. Your need is the amount where you wake without an alarm feeling human and do not crash mid-afternoon — discover it over a vacation week without alarms, then use it as the calculator's baseline. Optimizing against the wrong need produces optimized wrongness.