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  • Dr Paul Penn

The planning fallacy. How to beat one of procrastination’s enablers!

“All lies and jest, still a man hears what he wants to hear and disregards the rest” - Simon and Garfunkel.

In 2006 the German Government announced the construction of a new project: the Berlin Brandenburg Airport. It was intended to supersede the existing Tegel airport and expand Berlin’s capacity for air travel. The completion date for the project was anticipated to be in 2011 and construction was expected to cost around 2 billion euros. As of February 2020, the airport is still undergoing development and is currently projected to open this October with an estimated price tag of around 7 billion euros. Ouch! Well, I guess this puts any issues you might have had with the construction of your patio into context!

The Brandenburg Airport serves as an, admittedly extreme, example of the manifestation of a common psychological flaw called the planning fallacy (Kahneman & Tversky, 1977). This refers to a tendency to underestimate, often significantly, how long it will take to get a task done. Unfortunately, you don’t have to do anything quite so grand as be involved in the design of an airport to succumb to the planning fallacy. You’ll have first-hand experience of this if you’ve ever had to prepare an essay! The planning fallacy is a very relevant consideration in addressing procrastination when studying. If you underestimate the time required to complete a task, there is much less impetus not to leave it until the last minute. In this way, the planning fallacy serves as an enabler to our tendency to prefer doing tasks that offer small but immediate rewards over those that offer bigger rewards down the road (i.e. hyperbolic discounting) which I covered in the last blog.

Research in Psychology has often used the process of studying to investigate the planning fallacy in everyday life. The results often make for worrying, yet unsurprising, reading. For example, Buehler, Griffin and Ross (1994) asked final year students to predict when they would submit their thesis. They were then also asked for two further estimates (best- and worst-case scenarios). The experimenters then simply recorded when the students submitted their work. The average estimate given by the students for how long it would take them to complete their thesis was 33 days. Unfortunately, the average time taken by that same group of students to write their thesis was 55 days (i.e. 40% longer than the group’s average estimate).

You’d be forgiven for thinking that defeating the planning fallacy would be a simple matter of experience. After all, it’s hard to estimate the time required to complete a task if you don’t have relevant information upon which to base your judgements. Maxims like ‘older and wiser’ spring to mind. If only it were that easy! Buehler et al. found that the planning fallacy remained in evidence even when participants were explicitly cued to recall previous instances where their estimates for the completion of similar tasks had been way too optimistic. The problem the participants seemed to have was not so much a lack of experience, as a failure to use that experience to inform their subsequent estimates.

So, is there anything you can do to avoid succumbing to the planning fallacy? Happily, the answer is yes.

Kruger and Evans (2004) argued that the planning fallacy could be thought of as a *really* myopic internal perspective resulting in the size and complexity of a task being substantially under-represented. Think of the last time that you looked back on a completed task (e.g. writing an essay/report) in trying to estimate how long it would take you to complete a similar task in the here- and-now. Did you think of that task as a single entity, or did you break it down into its constituent sub-tasks? It turns out that doing the latter is critical in giving more realistic estimates of how long something will take to get done.

Kruger and Evans (2004) reasoned that if they could get people to unpack tasks into their constituent parts, the planning fallacy might shrink significantly. They conducted an experiment involving a task that entailed formatting a Word document. This formatting task was extensive and involved several sub-tasks, (e.g. changing margins, indenting paragraphs, highlighting text and attending to missed capitalisation). Before they were set to work, the participants were asked to estimate how long the task would take them. This is where the experimental manipulation came in. Half of the participants were instructed to unpack the task by listing all the changes required to the Word document before giving their estimates. The other half of the participants were asked to unpack the task after giving their estimates. The results indicated that unpacking the task before giving an estimate of its completion time reduced the size of the planning fallacy by more than half. Furthermore, the benefits of unpacking for the accuracy of estimates of completion increase with the size and complexity of the task at hand. So, next time you’re making that ‘To do’ list, get unpacking! If you represent what a task involves more accurately, your estimates of the time that task will take to complete will also become more accurate and you’re less likely to leave it until the last minute.

You can learn more about how to defeat procrastination in chapter two of my book: ‘The Psychology of Effective Studying: How to Succeed in Your Degree’ available direct from the publishers here (this link also features an order inspection copy facility for tutors/librarians). The book can also be purchased from or


Kahneman, D., & Tversky, A. (1977). Intuitive prediction: Biases and corrective procedures. Decisions and Designs Inc Mclean Va.

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.

Kruger, J., & Evans, M. (2004). If you don't want to be late, enumerate: Unpacking reduces the planning fallacy. Journal of Experimental Social Psychology, 40(5), 586-598.

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