What an All-Nighter Costs You

Staying up the whole night before an exam is a trade. You get extra hours with material you have not covered, and you pay for them in the exam and in the days after. This post covers what you gain, what it costs, and what to do if your exam is tomorrow.

What you gain from staying up

Some of the gain is real. If you have not read a chapter at all, reading it late is better than not reading it. Definitions, formulas and lists you go over in the night can still be there a few hours later, and for a paper that mostly asks you to recognise facts, that has value.

The catch is that the extra hours are your most tired ones, and sleep loss makes new material harder to take in. In one study, people who had been kept awake for a night studied new material the next day and remembered less of it than people who had slept normally (Yoo et al., 2007). Six hours in the middle of the night are worth less than six hours in the day.

How it affects you in the exam

An exam tests more than memory. You have to read each question carefully, keep the steps of a problem in your head, and catch your own mistakes before you write them down.

Attention and working memory are what sleep loss affects most clearly. A review of 70 studies of people kept awake for up to two days found the largest effects on simple attention and clear effects on working memory, while reasoning tests were barely affected (Lim and Dinges, 2010).

The attention problem shows up as lapses: short moments where nothing registers, between stretches where you work normally. In lab tests, performance became more uneven the longer the task went on (Doran et al., 2001), and an exam is a long task.

Sleep loss also makes you a poor judge of how you are doing. College students kept awake for 24 hours did worse on a critical-thinking test than students who had slept, yet rated their own concentration and effort higher and thought they had done better (Pilcher and Walters, 1997). If an exam feels as if it is going well after a night without sleep, do not rely on that feeling.

What it costs after the exam

Two costs carry on after the exam.

What you learned. Sleep after studying helps you keep what you studied, which is covered in how sleep helps you remember. In one small study, school students learned vocabulary in the evening and were then kept awake all night. Two days later they remembered less of it than when they had slept normally after learning, even though they had caught up on sleep in between (Gais, Lucas and Born, 2006). If the module continues next term, or this exam is a prerequisite for a later one, material learned at 3 a.m. is less likely to stay with you.

Recovery. After a single all-nighter, one long night of sleep seems to put most things right. In a lab study, people kept awake for 36 hours were back to normal on cognitive tests after one recovery night with 12 hours in bed, although they still reported feeling less energetic (Yamazaki et al., 2021). Several short nights in a row were harder to recover from: after five nights of four hours in bed, some attention measures had still not fully recovered after four long nights.

So the recovery cost is mainly time. The long night has to happen, and if you have another exam later in the week, it comes out of your preparation for that one.

When it does the least damage

An all-nighter does the least damage when:

• the paper mostly tests recognition and separate facts, such as drug classes, anatomical terms or dates;
• the module ends with this exam;
• you genuinely have not seen the material, so the choice is between some marks and none.

It does the most damage when:

• the paper is built on multi-step problems or long written answers, such as an engineering calculation, a proof or a law problem question, because these depend on the working memory and self-checking that sleep loss affects;
• the module is a prerequisite for something later;
• you have another exam in the same week.

If your exam is tomorrow

If you are already short of time, use a few hours well and then sleep.

1. Pick two or three topics that are likely to come up and that you can still learn tonight.
2. Test yourself on them: close your notes, write the answer, check it, and note what you missed. Testing yourself leads to better recall days later than rereading does, even though rereading makes people feel more confident (Roediger and Karpicke, 2006).
3. Decide before you start what time you will stop, and keep to it.
4. In the exam, leave a few minutes at the end to check each answer against its question.
5. After the exam, sleep long before you start on anything new.

How to avoid the next one

The night before turns into an all-nighter when revision starts from nothing, and the last night is when you find out what you do not know. Two habits make that less likely.

1. Spread the work out. Give each module a few short sessions a week in the fortnight before the exam. Spacing your practice out and testing yourself are the two techniques rated most useful in a large review of ten common study methods (Dunlosky et al., 2013).
2. Write down exactly what you got wrong, specifically enough to look it up again. In SymbioLearn, Mistakes does this for you: each quiz answer you get wrong is kept with the right answer and the line in your Source it came from, so the night before an exam starts from a short list and page numbers.

To work out the latest day you can start revising for your next exam without needing a late night, use the procrastination calculator.