Cone of Uncertainty

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The Cone of Uncertainty describes the change of uncertainties during a project. It goes back to research done by NASA which came to the conclusion that in the beginning of the project life cycle (i.e. before gathering of requirements) estimations have in general an uncertainty of factor 4. This means that the actual duration can be 4 times or 1/4th of the first estimations.

This factor can be quite different - depending on the character of the project: The more time the project spends on R&I the higher the factor.

With the duration of the project the uncertainty reduces but only reaches 0% with the projects end. The name "Cone of Uncertainty" comes from the initially fast, but later slow decrease of the uncertainty curve.

[edit] Consequences from the Cone of Uncertainty

Estimations (e.g. on duration, costs or quality) are very vague at the beginning of a project
Estimations and project plans based on estimations are to be redone on a regular base
Uncertainties can be introduced in estimations and should be visible in project plans