Draw/Progress Curves

Updated 5/13/21, 12/20/22

“Draw Schedules”, “Draw Curves”, “Completion Curves”, etc. typically all refer to the same thing. These curves are just a graphical representation of the percent we bill or work we put in place on a project per month through the course of construction.

“Draw” is used here because we are “drawing down” the construction loan. Our clients may ask for this forecast during preconstruction for multiple reasons. Sometimes they (or their consultants, financiers, etc.) need them to estimate and plan for construction loan interest reserves, a capitalized line item in the development budget). Or someone might want the curves to use as a project control document—by which they can monitor our progress once construction actually starts.

To simplify things, when we are making these forecasts most typically use a simple “S” curve (or “sigmoid”) to represent the cumulative progress—which is the same thing as a “bell” curve for monthly progress. The S curve shows that projects are slow at the start, fast in the middle, and slow at the end.

Obviously, reality will never be as clean as a perfect S curve. But projects do typically follow this shape. For example, here are the actual draws for a typical project (the scatterplot shows actual cumulative work complete for one of our project, the line shows a sigmoid function fit to that data using regression):

This means we can also use a project’s progress to date to help predict it’s future progress. If you fit a sigmoid to progress so far using regression, you can extend it out into the future and potentially adjust forecasts on that basis. Here is an example of a sigmoid regressed on data only extending to Month 10 (three key milestones are also shown):

One of these charts shows adjustment to the steepness coefficient, the other shows adjustment to the midpoint.

This also means issues with the job may show up in the curves. For example, here is a project that had a curtain wall default. The impact of this is obvious on the curve—the sigmoid is very steep up until Month 9 but after Month 9 is far flatter—and almost a straight line.

The typical expression of a sigmoid is expressed as a function of the midpoint of the curve (in the cases above, this would be expressed in months) and the steepness of the curve.

At the time of this writing, you can find an application for creating a new completion curve and reviewing old ones is located here:

https://constructioncurves.herokuapp.com/