Cone of uncertainty

How wide an honest estimate is at each stage: from 0.25× to 4× at the idea stage, narrowing as decisions are made.

Steve McConnell’s cone puts the spread of actual effort around an estimate at 0.25× to 4× at the initial concept, 0.5× to 2× with an agreed product definition, 0.67× to 1.5× with requirements written and 0.8× to 1.25× with the UI designed. And that is the best case: the cone narrows only if decisions actually get made.

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Related terms

Reference class forecasting: Estimating from what similar finished projects actually cost, instead of from your own feature list.
Fixed price: A contract where scope and price are agreed up front and the vendor carries the risk.

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