Sleep Debt Calculator (hours of sleep you are short)

Understanding the sleep debt calculator — concept and principle

This calculator adds up how much sleep you are short over a series of nights compared with the sleep you need. It shows the net debt, the hours missed on short nights, your average sleep and how many nights fell below your need.

Shortfalls minus extras: with the default inputs the result is 6.5 h (net sleep debt).

How it is calculated

Net sleep debt = Σ (need − hours slept) over all nights entered

Hours missed on short nights = Σ (need − hours slept) only for nights below your need

Average sleep = total hours slept ÷ number of nights

Average shortfall = need − average sleep

Nights with more sleep than you need reduce the net debt.

The principle

Sleep need is fairly stable for each person, so nights of short sleep build up a deficit that shows as sleepiness, slower reactions and poorer mood. The American Academy of Sleep Medicine and Sleep Research Society recommend 7 hours or more a night for adults. Research shows that sleeping in at the weekend does not fully undo the effects of a week of short nights, which is why both the net figure and the short-night total are shown.

Worked example

Default inputs: need 8 h; nights of 6.5, 6, 7, 6.5, 6, 8.5 and 9 h.

Shortfalls on short nights: 1.5 + 2 + 1 + 1.5 + 2 = 8 h over 5 nights.
Extra on long nights: 0.5 + 1 = 1.5 h.
Net debt = 8 − 1.5 = 6.5 h.
Average sleep = 49.5 ÷ 7 = 7.1 h; average shortfall = 8 − 7.07 = 0.9 h; nights entered 7.

How to read the result

A net debt of several hours a week is common and is a sign to move bedtime earlier or protect sleep time. Making up debt gradually with slightly longer nights is better than one very long lie-in. Your need can be estimated from how long you sleep on holiday after a few days without an alarm.

Common mistakes

Entering time in bed instead of time asleep.
Setting the need too low because you are used to short sleep.
Assuming one long weekend sleep clears the debt.

Keep in mind: This is a general estimate, not a diagnosis. Persistent sleepiness despite enough sleep can signal a sleep disorder and should be checked by a doctor.

Frequently asked questions

How much sleep do adults need?

7 hours or more a night is recommended; many people need 7–9.

Can I pay back sleep debt?

Partly, with longer sleep over several nights, but regular sleep is better than catching up.

Do teenagers need more sleep?

Yes, about 8–10 hours a night.

Sources: Watson NF, Badr MS, Belenky G, et al., "Recommended amount of sleep for a healthy adult: a joint consensus statement of the AASM and SRS", Sleep 2015;38(6):843–844 · Depner CM, Melanson EL, Eckel RH, et al., "Ad libitum weekend recovery sleep fails to prevent metabolic dysregulation during a repeating pattern of insufficient sleep and weekend recovery sleep", Curr Biol 2019;29(6):957–967

Checked 9 Nov 2026. Watson NF et al., “Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society”, Sleep 2015;38(6):843–844; Paruthi S et al., AASM consensus on sleep for children and teens, J Clin Sleep Med 2016;12(6):785–786; weekend recovery: Depner CM et al., Curr Biol 2019;29(6):957–967.

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