Sleep debt is the total of what you were short, night after night, against what you personally need. Most calculators assume you need eight hours. This one estimates your need from your own nights, which is what the app does.
Hours asleep, oldest night first. Estimate — nobody remembers exactly.
4h 30mbehind over 7 nights
- Your estimated need
- 7h 30m — the upper quarter of the nights you entered, on the reasoning that the long nights are the ones your body took when it could
- Your average
- 6h 48m a night
- What this means
- Enough to show up as a harder morning and a shorter fuse. One or two earlier nights closes most of it.
Older nights count half. A short night ten days ago matters less than one last night, so the number moves with what you did recently.
How the number is worked out
Three steps, and they are the same three the app runs.
- Your need comes from your long nights. Not eight hours, and not a survey average — the upper quarter of your recent nights, on the reasoning that the long ones are what your body took when nothing stopped it. It is held between seven and nine hours, because the evidence does not support a confident number outside that for adults.
- Each night short is added up. Sleeping longer than your need does not bank credit — you cannot get ahead, which is why the total only goes one way.
- Older nights count half. A short night ten days ago is not costing you what last night is.
What it is not
It is not a diagnosis and it is not a score. Under about two hours, the app does not mention it at all, because that is ordinary variation rather than a deficit worth acting on. If you are sleeping badly most nights, or you sleep long hours and still wake tired, that is a conversation with a doctor rather than an arithmetic problem — sleep apnoea and thyroid problems both look like sleep debt from the outside and neither is fixed by an earlier bedtime.
What the app does with it
The number on its own changes nothing, which is the honest limit of any calculator including this one. In IntentNorth the figure is read from Apple Health across fourteen nights without you typing anything, and then it does something: a short night shortens today’s session rather than cancelling it, the hard part is kept, and the reason is written on the change. It also moves the bedtime it suggests, never earlier than 8pm, because advice you would not follow is not advice.
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Educational only, never medical advice. This page stores nothing and sends nothing — there is no account, no database and no server behind it, so the numbers you type exist only in this tab. In Australia, Healthdirect is 1800 022 222 at any hour.