Sleep Debt Calculator
How much sleep you have accumulated a deficit of, and how long it realistically takes to clear.
Sleep debt is the difference between what you needed and what you got, accumulated.
How the sleep debt calculator works
Sleep debt is the difference between what you needed and what you got, accumulated. A 90-minute shortfall five nights a week builds 7.5 hours a week.
Recovery is not one-for-one. You cannot repay a large debt in a single long sleep — the evidence suggests it takes several nights of an extra hour or so, and some markers of impairment persist for longer. Preventing the debt is far more effective than repaying it.
Formula: debt = Σ(needed − actual)
Worked examples
| Inputs | Accumulated sleep debt | Note |
|---|---|---|
| 8 needed, 6.5 achieved, 14 days | 21 hours | 21 hours of debt |
| Meeting the need | 0 hours | no debt |
| A severe shortfall | 90 hours | 90 hours |
FAQFrequently asked questions
What is sleep debt?
The accumulated difference between the sleep you needed and the sleep you got.
Can I catch up at the weekend?
Partly. Two extra hours across a weekend covers about 3 hours against a 10.5-hour weekly deficit — the shortfall keeps growing.
How long does it take to recover?
Longer than most people expect. A large debt takes several nights of extra sleep, and some measures of performance stay impaired even after subjective alertness returns.
How much sleep do I actually need?
Most adults need 7 to 9 hours. The genuinely short sleepers who thrive on less are rare — far rarer than the number of people who believe they are one.
Does the debt keep accumulating forever?
The physiological effects saturate rather than growing without limit, but the impairment persists as long as the shortfall does.
Where these figures come from
- Mifflin MD et al., "A new predictive equation for resting energy expenditure in healthy individuals", Am J Clin Nutr 1990 — the BMR equation used here
- World Health Organization — Waist circumference and waist–hip ratio (2008 expert consultation) — waist-to-hip cut-offs
- Tanaka H, Monahan KD, Seals DR, "Age-predicted maximal heart rate revisited", J Am Coll Cardiol 2001 — 208 − 0.7 × age
- Nathan DM et al., "Translating the A1C assay into estimated average glucose values" (ADAG), Diabetes Care 2008 — eAG = 28.7 × A1c − 46.7
- Mosteller RD, "Simplified calculation of body-surface area", N Engl J Med 1987 — BSA = √(height × weight / 3600)
- NHS — national health guidance
Last checked: September 2026. The equations are fixed by their published papers and do not change with tax years or regulations; the thresholds quoted in verdicts name the body that set them.