Cognitive biases in planning & estimation

The biases, and how each one bites

• The planning fallacy

  You underestimate a task's time, cost, and failure odds even while recalling that similar past tasks overran.

• Optimism bias

  You treat the best case as the likely one and rate your project less at risk than comparable ones.

• Base-rate neglect

  You estimate from this project's vivid specifics and ignore how long similar projects actually took.

• Overconfidence effect

  Your confidence in an estimate far exceeds its accuracy, so buffers and ranges come out too narrow.

• Anchoring bias

  A rough first guess or an imposed deadline anchors the estimate; later adjustments stay too close.

• Sunk-cost fallacy

  Prior investment keeps you extending timelines on a failing plan instead of re-estimating from reality.

• Illusion of control

  You overestimate your grip on chance and dependencies, under-planning for external factors and slippage.

• Availability heuristic

  Risks easy to imagine get over-weighted while common but unimagined failure modes stay out of the plan.

• The curse of knowledge

  Knowing the work intimately, you can't picture a slower teammate, so you estimate it easier than it is for them.

• Hindsight bias

  After delivery you recall 'seeing it coming,' erasing the estimation errors you'd learn from next time.

Biases in other situations

Or browse the flip side — the mental models for real work →