Sleep calculator
Sleep debt calculator
Enter what you actually slept for the last few nights and your nightly target. The page adds up the shortfall and says how long clearing it takes at a rate you can sustain. Free, instant, no sign-up.
Your nights
Oldest first or newest first — the total is the same either way. Up to fourteen nights: past a fortnight this stops being a form and becomes a diary.
The number is the easy part. The coach works on which nights are recoverable and which are structural.
What sleep debt is
Sleep debt is the running total of the hours you fell short of your own target, and the reason it is worth tracking as a total is that the cost is cumulative. The performance price of six hours a night for a week is not the price of one bad night — it compounds across the week.
How this calculator works
Your nightly hours are summed, your target is multiplied by the number of nights entered, and the debt is the difference between the two. Negative means a surplus. The average per night and the per-night shortfall come from the same two totals. The recovery figure assumes one extra hour a night on top of hitting target, so the night count is simply the debt in hours rounded up — you cannot clear 3.2 hours of debt in three nights.
What an hour a night actually costs
Dinges' and Van Dongen's dose-response work is the reason this arithmetic is worth doing on paper. People restricted to six hours a night for two weeks performed as badly as people kept awake for two days straight — while rating their own sleepiness as only mildly elevated. The subjective sense of how impaired you are stops tracking the impairment. By the time the deficit is large enough to feel, it has been large enough to matter for a while.
Paying it back
This page does not claim debt is repaid hour for hour. Recovery sleep is denser — more slow-wave sleep early in the night, more REM later — so a nine-hour night after a bad week does more than one hour of good sleep does. But the research on how much more is not precise enough to publish a conversion factor, so no conversion factor is published here. What is also true: a lie-in on Saturday does not undo Monday to Friday. One extra hour a night on top of hitting target is the honest simple rate, and it is one most people can actually sustain.
Which number to watch
The total debt is the headline, but the per-night shortfall is usually the more useful figure, because it is the one you can act on tonight. A count of how many nights met target sits alongside it for a reason: two decent nights and five bad ones average out to the same number as seven mediocre ones, and they are not the same week.