S-curve diagram
A time-phased chart of the running total of costs, often tracing an S shape as work ramps up, peaks during execution, and tapers near closeout.
Key Points
- Shows cumulative costs (or value) plotted against time.
- Characteristic S shape: slow early spending, rapid growth mid-project, flattening at the end.
- Used to compare planned vs actual and earned value (PV, EV, AC) for variance analysis.
- Supports forecasting and stakeholder reporting through trend and baseline comparisons.
Example
A 9-month software project tracks planned cumulative spend (baseline) and actual cumulative spend each month. The S-curve reveals slower-than-planned spending in months 2-3, a rapid catch-up during months 4-6, and stabilization as the project enters testing and deployment.
PMP Example Question
Which chart best visualizes the running total of project budget over time for comparing planned and actual performance?
- Resource histogram
- S-curve
- Pareto chart
- Control chart
Correct Answer: B — S-curve
Explanation: An S-curve plots cumulative values over time, making it ideal for comparing planned vs actual costs or value.
HKSM