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After the week · Lesson 9 of 11

Catching Up After Short Nights: How to Repay Sleep Debt

Learn why one lie-in will not repay sleep debt, and how earlier bedtimes and a steady wake time help you catch up after short nights.

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Busy weeks happen to everyone. In this lesson you see what happens when you build up a sleep debt, and the best way to catch up. The research here comes mostly from short lab studies in healthy adults, so treat it as a guide, not a promise.

What sleep debt is

Sleep debt is the shortfall that builds when you sleep less than you need, night after night. Each short night adds a little more, and it grows faster than you feel it. By Friday you may only feel “a little tired” while the debt is much bigger than that. This is why “I feel fine” is a poor test of whether you slept enough.

Five red bars for Monday to Friday, each taller than the last, under the heading Sleep debt. On the right, a yawning face labelled Feels: a little tired, and a label that says Grows faster than you feel it.(opens the full-size picture)
The debt grows each night, while the face only looks a little tired.

One long night is not enough

In one lab study, people slept just four hours a night for five nights. Afterwards, even a ten-hour recovery night did not bring their attention fully back to normal. One big night of sleep helps, but it does not wipe the slate clean.

Five short red bars labelled 4 hours a night, then one tall green bar labelled 10 hours. A gauge called Attention has its needle between Low and Normal, short of the green Normal zone, with the label Not fully back to normal.(opens the full-size picture)
After five short nights, one 10-hour night did not fully restore attention.

The weekend trap

In another study, people slept five hours a night during the week, then slept as much as they liked at the weekend. Across three nights, they slept only about an hour more than usual, against more than twelve hours lost. Their body clocks also moved later, which can make the next week harder.

A tall red bar labelled More than 12 hours lost beside a very short green bar labelled About 1 hour caught up, with the note One week, lab study. On the right, two alarm clocks with an arrow between them and the label Moved later.(opens the full-size picture)
More than 12 hours lost, about 1 hour caught up, and a later body clock.

Repay it slowly

So repay it slowly. Go to bed a bit earlier for several nights, rather than having one long lie-in. Keep your weekend wake time within about an hour of your weekday one, and keep naps short. This fits what you learned on Night 1: a steady wake time protects your body clock.

Three day cards for Friday, Saturday and Sunday, each with a yellow moon, and the label Earlier bedtime above a sleeping person. On the right, a crossed-out card Lie-in until noon, and ticked labels Wake within 1 hour and Naps: short.(opens the full-size picture)
Earlier bedtimes for several nights, no lie-in, a wake time within an hour.

Expect Monday to be normal, not recovered

After a short week, expect Monday to be your first normal day, not a fully recovered one. You can repay sleep debt, but not hour for hour, and not in one weekend.

Three bars for Friday, Saturday and Sunday under the heading Sleep debt: the red part shrinks a little each day but never disappears. Beside them a Monday card with the labels First normal day, ticked, and Not hour for hour, crossed.(opens the full-size picture)
The debt shrinks over the weekend, but only part of the way.

Stop it growing

The best plan is to stop the debt from growing. Count your hours in your sleep diary instead of trusting how you feel. A week of numbers shows you quickly whether you are really getting the 7 or more hours adults need.

A sleep diary card listing hours slept for Monday to Sunday with a weekly total at the bottom, marked with a green tick. Beside it a smiling face labelled How you feel is crossed out, with the advice Count, don't guess.(opens the full-size picture)
Add up the hours in the diary. Do not guess from how you feel.

Drowsy at the wheel

After short nights, never drive when you are drowsy. If you feel your eyelids getting heavy, stop at the next safe place.

YOUR TURN

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Read the full lesson script

Busy weeks happen to everyone. In this lesson, you'll see what happens when you build up a sleep debt, and the best way to catch up.

Sleep debt is the shortfall that builds when you sleep less than you need, night after night. It grows faster than you feel it.

In one lab study, people slept just four hours a night for five nights. Afterwards, even a ten-hour recovery night didn't bring their attention fully back to normal.

In another study, people slept five hours a night during the week, then slept as much as they liked at the weekend. Across three nights, they slept only about an hour more than usual, against more than twelve hours lost. Their body clocks also moved later.

So repay it slowly. Go to bed a bit earlier for several nights, rather than having one long lie-in. Keep your weekend wake time within about an hour of your weekday one, and keep naps short.

After a short week, expect Monday to be your first normal day, not a fully recovered one. You can repay sleep debt, but not hour for hour, and not in one weekend.

The best plan is to stop the debt from growing. Count your hours in your diary, instead of trusting how you feel.

So remember: sleep debt builds faster than you feel. You can't repay it in one weekend. So go to bed earlier for a few nights, and keep your wake time steady. Before the next lesson, after your next short night, plan an earlier bedtime instead of a lie-in. In the next lesson, you'll see what sleep trackers and sleep aids can and can't do.