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?

  1. Resource histogram
  2. S-curve
  3. Pareto chart
  4. 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.

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