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About this tool
Log your last two weeks of sleep to see how many hours you owe, and get a realistic plan to repay it.
The Sleep Debt Calculator adds up how many hours you fell short of your nightly need across the last 7, 10 or 14 nights, letting nights you overslept offset the shortfall, and floors the result at zero. You set your need from an age band — 7 to 9 hours for adults aged 18 to 64 — log each night on a slider, and get your total debt, a severity band, your weekday-versus-weekend gap, and how many nights of extra sleep would clear it. It is for people who suspect they are running behind but have never put a number on it.
Open Sleep Debt Calculator on AltFTool — it loads instantly in your browser.
Set Your sleep need with the hours-per-night slider, or tap an age guideline — Teen (14–17), Adult (18–64) or 65 and over.
In Your sleep log pick the Most recent morning date and Nights to include (7, 10 or 14), then drag each night's slider in 15-minute steps.
Read Net sleep debt with its severity band, Average night, Total shortfall and Surplus banked, pick a repayment rate from +0.5h to +2h, then Copy report.
Hours slept above your need offset your deficit rather than being ignored, so a genuine catch-up weekend is reflected instead of the debt only ever going up.
It shows how many nights it takes to clear at +0.5, +1, +1.5 and +2 hours a night, so you can pick a rate you will actually keep to.
It averages your work nights and free nights separately and reports the gap, which is what a chronic short-sleep pattern looks like before the total gets alarming.
Debt is the sum of (nightly need − hours actually slept) across the window you choose, with nights you slept more than your need subtracting from the total, and the result never going below zero. Seven nights at 6 hours against an 8-hour need is 14 hours of debt.
For most adults aged 18 to 64 it is 7 to 9 hours a night; teenagers aged 14 to 17 need 8 to 10, and adults 65 and over typically 7 to 8. Your own figure sits somewhere in that range, so pick the point where you wake without an alarm feeling rested.
Partially, and only for small debts. Adding an extra hour a night clears a 5-hour debt in about five nights, but a 20-hour debt takes roughly 20 nights at that rate — which is why one long Saturday does not undo a bad fortnight. Very long lie-ins also shift your body clock and make the following Monday worse.
If you are consistently 20 or more hours behind, if you are having attention lapses or nodding off during the day, or if you cannot sleep even when you have the opportunity, it is worth medical attention rather than more discipline. This tool is informational and does not diagnose anything — persistent insomnia, snoring with daytime sleepiness, or suspected sleep apnoea should be assessed by a doctor.
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