Question 1

What is sleep debt?

Accepted Answer

Sleep debt is the cumulative difference between the sleep your body needs and the sleep you actually get. If you need 8 hours but consistently sleep 6, you accumulate 2 hours of debt per night — 14 hours over a week. Sleep debt affects cognitive performance, mood, immune function, metabolism, and long-term cardiovascular health.

Question 2

How long does it take to recover from sleep debt?

Accepted Answer

Research published in Current Biology found it takes approximately 3 nights of recovery sleep to restore performance after 5 nights of mild restriction. For mild debt (under 7 hours), substantial recovery is possible within 2 to 4 nights of extended sleep. Gradually extending sleep by 1 to 1.5 hours per night is more effective than a single long sleep.

Question 3

Can weekend lie-ins cancel out weekday sleep debt?

Accepted Answer

Partially. Weekend recovery sleep can restore some cognitive functions reduced by weekday restriction. However, social jetlag — the mismatch between weekday and weekend sleep schedules — can disrupt your circadian rhythm. The NHS recommends maintaining a consistent sleep schedule even on weekends as the most effective long-term strategy.

Question 4

What are the health risks of chronic sleep debt?

Accepted Answer

Chronic sleep debt is linked to: increased risk of type 2 diabetes and obesity, cardiovascular disease and hypertension, weakened immune system, depression and anxiety, impaired memory and decision-making, increased accident risk, and accelerated biological ageing.

Question 5

How accurate is this sleep debt calculator?

Accepted Answer

The calculator uses age-based targets from the NHS, the National Sleep Foundation and the American Academy of Sleep Medicine. The debt and recovery calculations are mathematically precise based on the hours you enter. Sleep need is individual — if you have persistent fatigue despite adequate sleep, speak to your GP to rule out conditions such as sleep apnea.

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