How much sleep have you lost this week?

Mostly no. Studies show one or two long nights of recovery sleep do reduce same-week sleep pressure, but the cognitive and metabolic impairments from chronic short sleep do not fully reverse with weekend catch-up. The calculator treats surplus as zero because that is the conservative read of the evidence — pretending you banked credit will keep you from fixing the schedule.

Beyond twelve weeks, the recovery model breaks down. Sleep debt over that horizon almost always means a chronic schedule problem — shift work, parenting, untreated insomnia — and the fix is fixing the schedule, not catching up. If you hit the cap, the recommendations point you toward the underlying behaviour change.

The defaults match the National Sleep Foundation consensus ranges. If you wake naturally without an alarm after seven hours and feel sharp all day, your target is seven, not seven and a half. Override the target field. Anything below five or above eleven is unusual enough that the form refuses it — see a clinician if you are confident in those numbers.

Not for the total. The calculator sums deficits regardless of which night had what. The per-night breakdown is shown so you can spot patterns — for example, weekend recovery hiding weekday restriction. Enter oldest night first if you want the chart to read left-to-right chronologically.

Yes. Add nap minutes to the same-day overnight sleep, expressed in hours. A 20-minute nap is 0.33h. Naps under 30 minutes do help with daytime alertness but do not fully substitute for nighttime sleep — so the rolled-up number is approximate. For severe debt, the recommendation to schedule a short afternoon nap stands.

The bands track behavioural and physiological markers that emerge in chronic sleep restriction studies. Mild (1-2h average deficit) shows mood and concentration declines. Moderate (2-3h) shows reaction-time impairment comparable to mild alcohol intoxication. Severe (3h+) shows the immune, metabolic, and accident-risk markers that drive the public-health concern around sleep loss.