What sleep debt is
Sleep debt is the accumulated difference between the sleep you need (typically 7–9 h for adults) and what you actually got. Chronic debt does more than make you tired: it degrades memory consolidation, immune function, glucose regulation and mood — and studies consistently show it cannot be fully "repaid" in one weekend.
How recovery works
- Acute debt (a few nights) recovers fast: one long night plus a short nap usually clears it.
- Chronic debt (weeks of 6 h nights) needs 1–2 weeks of consistently longer sleep — and even then, some cognitive effects linger.
- Sleeping in on weekends helps partially, but shifting your schedule back and forth creates social jet lag — a separate cost.
- Consistency beats heroics: 7.5 h every night beats 5 h + 12 h catch-up.
Honest recovery math
The calculator assumes you can bank extra sleep at the pace you pick (e.g. +1 h/night). If you owe 14 h, that's 14 nights of +1 h — about two weeks. If that sounds like a lot, that's the point: debt is expensive. The cheapest fix is preventing it, not repaying it.