Sleep Debt Calculator
Enter your last seven nights of sleep and your age. You get the total you are short against the recommended range, which nights caused it, and how many nights of extra sleep it takes to clear.
Adult (26-64): 7–9 h
Leave blank for the middle of your age range.
Hours slept, last 7 nights
Sleep debt this week
8 h 30 min
after 30 min of catch-up
Average per night
6 h 47 min
need 8 h
Short nights
5
of 7
Nights to recover
9
at +1 h a night
| Night | Slept | Need | Shortfall |
|---|---|---|---|
| Mon | 6.5 h | 8 h | −1 h 30 min |
| Tue | 6 h | 8 h | −2 h |
| Wed | 7 h | 8 h | −1 h |
| Thu | 5.5 h | 8 h | −2 h 30 min |
| Fri | 6 h | 8 h | −2 h |
| Sat | 8.5 h | 8 h | +30 min |
| Sun | 8 h | 8 h | 0 |
What a shortfall adds up to
Nightly shortfall against an 8-hour need, accumulated over a week and a month, and the nights needed to clear it at an extra hour a night.
| Sleeping | Short per night | Debt per week | Per month | Nights to clear a week |
|---|---|---|---|---|
| 7.5 h a night | 30 min | 3 h 30 min | 15 h | 4 |
| 7 h a night | 1 h | 7 h | 30 h | 7 |
| 6.5 h a night | 1 h 30 min | 10 h 30 min | 45 h | 11 |
| 6 h a night | 2 h | 14 h | 60 h | 14 |
| 5.5 h a night | 2 h 30 min | 17 h 30 min | 75 h | 18 |
| 5 h a night | 3 h | 21 h | 90 h | 21 |
What the debt costs, by size
| Debt | Typical effect | Comparable to |
|---|---|---|
| 1–2 h | Slightly slower, a little irritable; most people don't notice. | A mild cold |
| 3–5 h | Measurable drop in reaction time and attention; cravings for sugar and caffeine. | One late night, felt for two days |
| 6–10 h | Performance like one full night without sleep; you rate yourself as fine. | Blood alcohol around 0.05% |
| 10 h+ (chronic) | Insulin resistance markers, higher blood pressure, weaker immune response, low mood. | Shift work without recovery |
Effect sizes from Van Dongen et al. (2003) and Dawson & Reid (1997); the alcohol comparison is the 17-to-19-hours-awake equivalence from the latter.
Paying it back without wrecking the schedule
- Move bedtime earlier, not wake time later. An earlier night adds sleep without shifting your body clock; a late morning shifts it and makes the next night harder.
- Cap the weekend lie-in at an hour. More than that and Monday morning is jet lag.
- A 20-minute afternoon nap takes the edge off without touching tonight; a 90-minute one pays down real debt but only if it ends by mid-afternoon.
- Recalculate weekly. Debt is a rolling number; the point of tracking it is to catch the 6-hour weeks before they become the habit.
Frequently Asked Questions
What is sleep debt?
The running total of sleep you needed and did not get. Sleep 6 hours a night when you need 8 and you accrue 2 hours a night, 14 a week. It is not a metaphor: reaction time, glucose regulation and mood track the cumulative shortfall, not just last night. Van Dongen's 2003 study found two weeks of 6-hour nights impaired performance as much as one full night without sleep -- and the subjects did not feel that impaired.
Can I pay it back on the weekend?
Partly. Sleeping in 2 or 3 hours on Saturday and Sunday recovers some of a modest weekday debt, and the calculator counts those as catch-up. But it does not fully reverse a week of short nights, and a big weekend shift moves your body clock so Monday is worse. Better to add an hour a night through the week than three on Sunday.
How long does recovery take?
Plan on one night of recovery per hour of debt, sleeping an extra hour each night -- so a 5-hour debt takes about five nights. Kitamura et al. (2016) found people who habitually short-slept needed several nights of unrestricted sleep just to reach their true need, so long-standing debt takes longer than the arithmetic suggests.
Does sleep debt ever expire?
Not in the sense of going away unpaid. The acute effects fade over a couple of weeks of good sleep, and the body does not carry a ledger back years. But the health effects of chronic short sleep -- cardiovascular, metabolic, immune -- accumulate over years, which is what makes the habit rather than any one week the thing to fix.
These calculators use published sleep-science guidelines and are for general guidance. They are estimates, not medical advice: persistent insomnia, loud snoring or gasping in sleep, or daytime sleepiness that affects driving are reasons to see a doctor, not to adjust a bedtime.