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Helping students overcome the planning fallacy

The planning fallacy tells us that everything will take longer than we think it will (Kahneman & Tversky, 1982). In a fun—and unpublished—study, MIT graduate student Kaley Brauer, tells us about what they learned about the planning fallacy—albeit never named as such—when a “small group of postdocs, graduate students, and undergraduates inadvertently formed a longitudinal study contrasting expected productivity levels with actual productivity levels.”

It all started in an effort to be more productive by holding each other accountable. Once a week this group would get together to declare what tasks they wanted to accomplish for the following week and report on what they had accomplished the previous week. As part of this accountability, each person was asked to predict how long each task would take and then report on how long each task actually took.

Nine months and “559 self-reported tasks” later, the data are interesting if not surprising. “The actual number of hours required to complete a task is, on average, 1.7x as many hours as expected (with a median multiplier of 1.4x).” The worst estimates were for tasks related to writing and coding. The best estimates were for tasks that had a set deadline.

To help ourselves overcome the planning fallacy, there are three things we can do. First, break the task down into its component parts and estimate how long each component will take. When we do this, our predicted times to completion are more accurate (Forsyth & Burt, 2008; Kruger & Evans, 2004). Second, make a plan. When we decide when and where we are going to do these subtasks, we are more likely to complete them in the time predicted (Koole & van’t Spijker, 2000). Lastly, when we are working on the task, getting rid of distractions and interruptions—phones set to silent!—will help us finish the darn thing in the time we predicted (Koole & van’t Spijker, 2000).

After sharing information with your students about the planning fallacy and how to mitigate it, ask your students to take a look at the assignments remaining in your course. Send students into small groups to break down each assignment into smaller, component parts, and provide a time estimate on how long they think each part would take to complete. As a “deliverable,” ask each student to submit a work plan for each component. For each remaining assignment (or, perhaps, just one large assignment), for each subcomponent, note how long they think it will take to complete and identify where and when they will do this subcomponent task. If you’d like to do a follow-up, ask students to keep track of how long it actually takes them to complete each subcomponent task, and submit this information when they submit their assignment(s).

Giving students some practice with this skill now may benefit them enormously in the long run.



Forsyth, D. K., & Burt, C. D. B. (2008). Allocating time to future tasks: The effect of task segmentation on planning fallacy bias. Memory and Cognition, 36(4), 791–798.

Kahneman, D., & Tversky, A. (1982). Intuitive prediction: Biases and corrective procedures. In D. Kahneman & A. Tversky (Eds.), Judgment Under Uncertainty: Heuristics and Biases (pp. 414–421). Cambridge University Press.

Koole, S., & van’t Spijker, M. (2000). Overcoming the planning fallacy through willpower: Effects of implementation intentions on actual and predicted task-completion times. European Journal of Social Psychology, 30(6), 873–888.<873::AID-EJSP22>3.0.CO;2-U

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.

Source: macmillan psych community