One of the most widely used tools project controls professionals use to evaluate a project’s health is the S-curve. This chart is designed to compare three primary indicators of a project’s progress and status. Which are, Budget, Actual Cost and Earned Value (or Progress). With these three key metrics, the system can then calculate a forecast of how the project will play out from any point in time.
The S-Curve is therefore made up of four (4) or more individual lines on a chart:
- Budget curve
- Actual cost curve
- Earned Value curve (also known as the progress curve)
- Forecast curve
Watch this brief video on creating an S-Curve in 4castplus.
S-Curves in Construction Project Controls
Although the S-Curve is used in many applications – from business to education to project management – the version we’re discussing is related to construction project controls and project management. It’s a key element of Earned Value Management (EVM) as a core method for monitoring the health of the project. The reason it’s called an “S” curve is because construction projects typically start slow, then ramp up quickly, then taper off at the end – thereby reflecting the “S” pattern.
The curve for the budget line is defined by merging project cost with schedule. This displays the total budget over a timeline, which is an important factor when assessing whether the project is operating to the original plan or deviating off course. 4castplus also provides tools to override the schedule as the time component to draw the curve. The first tool is called “Time Phasing”, and is designed to enable project controls to input a more realistic cash flow plan for any budgeted activity on the project.
As actual costs are incurred on the project, the “Actuals” curve will display alongside the budget curve to compare these two with each other. Clearly, the ideal scenario is if they are very closely aligned – which would indicate the project is incurring cost at the same pace as initially budgeted. The Earned Value curve provides a third dimension, which is physical progress. By incurring cost doesn’t necessarily mean the project is progressing as planned – it’s possible to spend money without getting things done.
With these three dimensions, the system can calculate a vast array of earned value management (EVM) metrics such as: CPI, CV, ETC, EAC, SPI and much more. The system will, in fact, use the cost performance index (CPI) to draw the estimate-to-complete (ETC) curve, which is a calculated forecast.