Cone of Uncertainty

March 25, 2021

The Cone of Uncertainty is a project management concept.

First, we plot the progress of project over time with time on the X-axis and amount of work completed on the Y-axis

We see the progress of a project that start out rapidly completing work then had a bit of a lull before finding a steady pace again

Then, we can identify the fastest possible pace and the slowest possible pace for the project by drawing lines that contain our progress line. These correspond to the worst and best case for the average performance over time.

We see that additional lines showing worst and best case performance.

If we draw lines for the worst and best case performance at the end of our progress line, we draw the “cone of uncertainty”: a zone representing the possible status for our project in the future.

The lines for best and worst case performance form top and the bottom edge of the “cone” of uncertainty

We can now use this “cone of uncertainty” to answer questions about our project.

If we want to ask “when will the project be done,” we can draw a horizontal line across the chart for some definition of done and see where it intersects the cone.

The horizontal grey line represents some definition of done. The points where this line intersects with the cone represent the range of potential completion dates from optimistic to pessimistic.

Alternatively, we can ask “how much work will be complete by a given day” by drawing a vertical line at the given day and seeing where that line intersects the cone.

The horizontal grey line represents a deadline. The points where this line intersects the cone represent the range of potential amount of completed work from optimisitc to pessimistic.

Return home