Why your revision plan always runs late, and how to fix it

You made a revision timetable. It had colours. By day four it was wrong, and by the weekend you'd stopped looking at it. That isn't a character flaw. Psychologists have a name for it, and the research behind the name also points to a fix.

34 days, then 56

In a classic set of studies, psychologists Roger Buehler, Dale Griffin and Michael Ross asked university students writing a final-year thesis when they expected to finish (Journal of Personality and Social Psychology, 1994). Their best guess, on average, was 33.9 days. The real average was 55.5 days.

Fewer than a third (29.7%) finished by their best guess. The researchers also asked for a worst-case date. The average worst case was 48.6 days, and still only about half of the students (48.7%) finished by it. Even the pessimistic plan was too hopeful.

This pattern is called the planning fallacy: we underestimate how long our own tasks will take, even when we have done similar tasks before and they ran late then too.

Why it happens

The same paper looked at what people think about while they plan. When students talked through their predictions out loud, they mostly described how the work would go: first this, then that. They rarely brought up how long similar jobs had taken them in the past. And when a past plan had failed, they tended to blame a one-off: a cold, a busy week, a surprise test.

Two more findings matter for students. People were optimistic about their own tasks but not about other people's: observers guessed that others would take longer, and used past experience more. And in one of the studies, the optimistic bias disappeared when people were asked to connect their past experiences to the new prediction before making it.

How to plan for the late version

1. Start from the last time, not the plan. Before you write a timetable, write down how long the last similar thing really took. Last term's history essay, the last chapter you revised. That number is your starting point.
2. Add a buffer you can see. In the thesis study, the real time ran more than 60% over the best guess. You don't need that exact figure, but planning to finish with roughly a third of your days spare is a simple rule that leaves room for the bad Tuesday.
3. Ask someone else. Observers in the study were better at guessing other people's time than people were at guessing their own. Ask a parent or friend how long they think it will take you, and take the longer answer.
4. Count the days, not the weeks. "Three weeks" feels roomy. Twenty-one days minus weekends you'll be away minus the day of the party is clearer. A countdown with every paper on it, like our free exam countdown, makes the real number hard to ignore.
5. Do the first small piece today. The plan can be wrong, but a task already started is easier to finish. If the first step is too big, break it down with Tiny steps.

What a realistic revision week looks like

Say you have five papers in three weeks. Instead of giving each subject an equal block and hoping, list the papers by date, give the first ones more of the early days, and leave the last two or three days before each paper light. Then look back at the end of each week: what took longer than planned? Move the rest of the plan, not your bedtime.

For more on the last stretch, see the last week before an exam and the evening between two papers. If you are a parent of a child with ADHD, our sister blog has a post on time blindness, which makes all of this harder.

Sources

• Buehler, R., Griffin, D., & Ross, M. (1994). Exploring the "planning fallacy": Why people underestimate their task completion times. Journal of Personality and Social Psychology, 67(3), 366-381.