How much sleep do you owe?

What sleep debt is

Sleep debt is the gap between the sleep you need and the sleep you get. It adds up night by night: six short nights of an hour each leave you six hours behind, even if no single night felt bad.

Most adults need seven to nine hours. Losing an hour or two a night often doesn't feel dramatic, because people get used to feeling a little tired and stop noticing it.

Why one big lie-in doesn't fix it

Sleeping in at the weekend feels like catching up, and it helps a little. But a 2019 study (Depner et al., Current Biology) found that weekend recovery sleep did not undo the effects of a short-sleep week, and the late lie-ins pushed people's body clocks later, making Monday harder.

A steadier approach works better: a slightly earlier bedtime for several nights, with the same wake time every day.

How to pay it back

• Go to bed 30–60 minutes earlier for the next week or two, rather than sleeping late.
• Keep your wake time the same, weekends included. It's the anchor for your body clock.
• Guard the first hour of bed: lights low, phone away, the same short routine every night.
• A short nap is fine: 20 minutes, before mid-afternoon, so it doesn't push bedtime later.

Common questions

Can I ever fully catch up?

Recent, short-term debt can be paid back over a week or two of longer nights. The bigger win is stopping it from building up again.

Do extra hours on one night cancel out a short one?

Partly. This calculator nets them off, but a big swing between nights still unsettles your body clock.

I sleep enough hours but still feel tired. Why?

Hours aren't everything: fragmented sleep, timing that fights your body clock and alcohol all matter. If tiredness persists, it's worth speaking to a healthcare professional.

Find out what's wrecking your sleep →