Sleep Debt Calculator

Losing an hour a night does not feel like much on Tuesday. By Friday it is most of a full night, and a long Saturday morning only pays part of it back. Sleep debt is that running total: the gap between the sleep you need and the sleep you actually got.

Type how long you slept on each of the last seven nights, as6.5 or6:30, and how much you need. The page shows every night against that need, the debt left for the week, and how quickly a slightly earlier bedtime would clear it.

Worked Example: a Short Week and a Weekend Lie-In

The page opens on someone who needs 8 hours and slept 6.5, 6, 7, 5.5 and 6.5 hours from Monday to Friday, then 9 and 8.5 at the weekend. That is 49 hours against 56 needed, a 7-hour debt, with an average of exactly 7 hours a night. The weekday nights fell 8 h 30 min short in total; the weekend won back 1 h 30 min of that and no more.

At the default of 60 extra minutes a night the debt clears in about 7 nights; at 30 minutes it takes 14. Load Sample cycles through a nearly even week, a teenager who needs 9 hours, a new parent 17 hours behind, and a week with more sleep than needed, typed in h:mm.

How the Math Counts Debt Two Ways

• Net debt = need × nights logged − hours slept. A long night offsets a short one, so this is what is still owed.
• Shortfall before catch-up adds up only the nights that fell short. The gap between the two is what long nights won back.
• Recovery = net debt ÷ extra minutes a night, rounded up to whole nights.
• Nights left blank are skipped rather than counted as zero, so a week with a missing night still works.

The average card also counts nights under 7 hours, the minimum the American Academy of Sleep Medicine and the Sleep Research Society recommend for adults. A need outside 4 to 12 hours stops with“Sleep need must be between 4 and 12 hours a night, e.g. 8 or 7:30.”

When Not to Use This Instead of a Doctor

Paying the hours back is not the same as undoing the effects. A 2019 University of Colorado trial found that sleeping in at the weekend did not prevent the metabolic changes caused by short weeknights, which is why the recovery plan suggests a little extra every night rather than one long lie-in.

If you are tired whatever you sleep, snore loudly, wake gasping, or cannot sleep even with the time to do it, the cause is unlikely to be arithmetic. Those are reasons to speak to a doctor about insomnia or sleep apnoea.