★ HEALTH · SLEEP · SLEEP DEBT
You owe 5.50 hours of sleep a week. You need 56.00 hours a week and you get 50.50 hours — 6.5 hours on weeknights and 9 hours at the weekend — so the debt is 5.50 hours, and it takes 5.50 nights at one extra hour a night to repay. Enter your own sleep to work out what you owe.
Sleep debt is the gap between the sleep you need and the sleep you get. The week needs seven nights of your target, and the week gives you five weeknights and two weekend nights. This calculator works out the weekly need, the weekly actual, the debt, and how many nights of extra sleep repay it — so the number you get is the number of hours you owe.
Sleep debt is the gap between the sleep you need and the sleep you get. The weekly need is seven nights of your target: seven times the target sleep a night. The weekly actual is five weeknights plus two weekend nights: five times the weeknight sleep plus two times the weekend sleep. The debt is the weekly need minus the weekly actual: a positive number is hours owed, and a negative number is a surplus, not a debt. The average night is the weekly actual divided by seven. The recovery is the debt divided by the extra sleep a night: the nights it takes to repay the debt at one extra hour a night, or at two extra hours a night.
At the defaults — target 8 h a night, weeknight 6.5 h, weekend 9 h, extra 1 h a night — the weekly need is 7 × 8 = 56.00 h, the weekly actual is 5 × 6.5 + 2 × 9 = 50.50 h, the debt is 56.00 − 50.50 = 5.50 h, the average night is 50.50 ÷ 7 = 7.21 h, and the recovery is 5.50 ÷ 1 = 5.50 nights at one extra hour a night, or 5.50 ÷ 2 = 2.75 nights at two extra hours a night.
| Case | Need | Actual | Debt | Average night |
|---|---|---|---|---|
| Default (8 h target) | 56.00 h | 50.50 h | 5.50 h | 7.21 h |
| Weeknight 7 h | 56.00 h | 53.00 h | 3.00 h | 7.57 h |
| Weekend 7 h | 56.00 h | 46.50 h | 9.50 h | 6.64 h |
| Target 7 h | 49.00 h | 50.50 h | -1.50 h (surplus) | 7.21 h |
| Target 9 h | 63.00 h | 50.50 h | 12.50 h | 7.21 h |
| Weeknight 5 h | 56.00 h | 43.00 h | 13.00 h | 6.14 h |
Setup: target 8 h a night, weeknight 6.5 h, weekend 9 h, extra 1 h a night.
Line 1 — the weekly need. 7 × 8 = 56.00 h of sleep a week.
Line 2 — the weeknight sleep. 5 × 6.5 = 32.50 h across the five weeknights.
Line 3 — the weekend sleep. 2 × 9 = 18.00 h across the two weekend nights.
Line 4 — the weekly actual and the debt. 32.50 + 18.00 = 50.50 h of sleep a week, so 56.00 − 50.50 = 5.50 h of debt.
Line 5 — the average night and the recovery. 50.50 ÷ 7 = 7.21 h a night on average, and 5.50 ÷ 1 = 5.50 nights at one extra hour a night, or 5.50 ÷ 2 = 2.75 nights at two extra hours a night.
Weeknight 7 h: the weekly actual rises to 5 × 7 + 2 × 9 = 53.00 h, so the debt falls to 56.00 − 53.00 = 3.00 h, and the average night rises to 53.00 ÷ 7 = 7.57 h. Half an hour more on each weeknight takes 2.50 hours off the weekly debt.
Weekend 7 h: the weekly actual falls to 5 × 6.5 + 2 × 7 = 46.50 h, so the debt rises to 56.00 − 46.50 = 9.50 h, and the average night falls to 46.50 ÷ 7 = 6.64 h. Two hours less on each weekend night adds 4.00 hours to the weekly debt, because the weekend is only two nights but each one counts double.
Target 7 h: the weekly need falls to 7 × 7 = 49.00 h, while the actual stays 50.50 h, so the debt is 49.00 − 50.50 = -1.50 h — a 1.50-hour surplus, not a debt. A lower target turns the same sleep into a surplus: the model shows a surplus whenever the actual beats the need.
Target 9 h: the weekly need rises to 7 × 9 = 63.00 h, while the actual stays 50.50 h, so the debt rises to 63.00 − 50.50 = 12.50 h. One hour more a night on the target adds 7.00 hours to the weekly debt.
Weeknight 5 h: the weekly actual falls to 5 × 5 + 2 × 9 = 43.00 h, so the debt rises to 56.00 − 43.00 = 13.00 h, and the average night falls to 43.00 ÷ 7 = 6.14 h. A short weeknight is the dearest habit here: five short nights cost more than two short weekend nights.
Extra — the same pattern for 4 weeks: the debt is 5.50 × 4 = 22.00 h owed over four weeks, which is about 2.75 full nights of sleep at 8 hours a night. A debt that looks small in a week is a whole weekend of sleep in a month.
Reverse — the break-evens: the weeknight sleep breaks even at 7.60 h — 5 × 7.60 + 18.00 = 56.00 h. The weekend sleep breaks even at 11.75 h — 32.50 + 2 × 11.75 = 56.00 h, which is more than most people sleep, so the weekend alone cannot fix a short week. And the target breaks even at 7.21 h a night — 50.50 ÷ 7: a target at or below 7.21 h a night leaves no debt on this sleep.
The model assumes the same sleep every weeknight and the same sleep every weekend night, seven nights a week, and a single target for every night. It assumes the week runs Sunday to Thursday for weeknights and Friday and Saturday for weekend nights. Naps are not counted: a nap does not change the weekly actual here, because the model counts night sleep only. A negative debt is a surplus, and it is shown as one, not as a debt. This is a simple hours model, not a medical assessment: it counts hours, not sleep quality, and it cannot say whether you are well rested. If you are worried about your sleep, talk to a clinician. Rounding convention: hours to 2 decimals, nights to 2 decimals, and all figures are computed from unrounded values, rounded only for display.
| Output | Formula | What it means |
|---|---|---|
| Weekly need | 7 × target | 56.00 h. |
| Weekly actual | 5 × weeknight + 2 × weekend | 50.50 h. |
| Sleep debt | need − actual | 5.50 h. |
| Average night | actual ÷ 7 | 7.21 h. |
| Repay at +1 h/night | debt ÷ extra | 5.50 nights. |
| Repay at +2 h/night | debt ÷ 2 | 2.75 nights. |
| Weeknight 7 h | same model, weeknight 7 h | Actual 53.00 h, debt 3.00 h, average 7.57 h. |
| Weekend 7 h | same model, weekend 7 h | Actual 46.50 h, debt 9.50 h, average 6.64 h. |
| Target 7 h | same model, target 7 h | Need 49.00 h, actual 50.50 h, 1.50-hour surplus. |
| Target 9 h | same model, target 9 h | Need 63.00 h, debt 12.50 h. |
| Weeknight 5 h | same model, weeknight 5 h | Actual 43.00 h, debt 13.00 h, average 6.14 h. |
| Extra: 4 weeks | debt × 4 | 22.00 h owed, about 2.75 full nights. |
| Reverse: break-even weeknight | (need − 2 × weekend) ÷ 5 | 7.60 h. |
| Reverse: break-even weekend | (need − 5 × weeknight) ÷ 2 | 11.75 h. |
| Reverse: break-even target | actual ÷ 7 | 7.21 h/night. |
The math is exact for the numbers you enter: the weekly need is seven times the target, the weekly actual is five times the weeknight sleep plus two times the weekend sleep, the debt is the need minus the actual, and the recovery is the debt divided by the extra sleep a night. What the model cannot do is measure how well you sleep: it counts hours, not sleep quality, and a long night of broken sleep is not the same as a long night of deep sleep. Naps are not counted, and this is a simple hours model, not a medical assessment. It assumes the same sleep every weeknight and the same sleep every weekend night. For your sleep timing, see sleep cycle calculator; for a general health check, see BMI calculator.
Bright Side Kit. "Sleep Debt Calculator: Hours Owed & Recovery Time 2026." https://brightoolbox.com/sleep-debt-calculator/ Accessed October 25, 2026.5.50 hours a week at the defaults. You need 56.00 hours a week and you get 50.50 hours — 6.5 hours on weeknights and 9 hours at the weekend — so the debt is 56.00 − 50.50 = 5.50 hours, and it takes 5.50 nights at one extra hour a night to repay.
Weekly need minus weekly actual. The need is 7 × 8 = 56.00 hours, the actual is 5 × 6.5 + 2 × 9 = 50.50 hours, and the debt is 56.00 − 50.50 = 5.50 hours. The average night is 50.50 ÷ 7 = 7.21 hours.
5.50 nights at one extra hour a night. The debt is 5.50 hours, so 5.50 ÷ 1 = 5.50 nights at +1 hour a night, or 5.50 ÷ 2 = 2.75 nights at +2 hours a night.
The debt falls to 3.00 hours. The weekly actual rises to 5 × 7 + 2 × 9 = 53.00 hours, so the debt is 56.00 − 53.00 = 3.00 hours, and the average night rises to 7.57 hours. Half an hour more on each weeknight takes 2.50 hours off the debt.
Yes — that is a surplus, not a debt. With a target of 7 hours a night the need is 49.00 hours while the actual is 50.50 hours, so the debt is −1.50 hours, which is shown as a 1.50-hour surplus. A negative debt means you sleep more than your target.
7.60 hours on weeknights, or a target of 7.21 hours. The break-even weeknight sleep is 7.60 hours, the break-even weekend sleep is 11.75 hours — more than most people sleep — and the break-even target is 7.21 hours a night, which is the average night itself.
22.00 hours over 4 weeks. The weekly debt is 5.50 hours, so 5.50 × 4 = 22.00 hours over four weeks, which is about 2.75 full nights of sleep at 8 hours a night.
No, not in this model. Naps are not counted: the weekly actual counts night sleep only — five weeknights and two weekend nights. This is a simple hours model, not a medical assessment, and it counts hours, not sleep quality.