Primavera P6 S-Curve.
Cost and physical-progress cumulative curves are how project controls tells the story of the project each month. Slippage shows up on S-curves before it shows up on the critical path — and that is why every monthly report has one at the top.
Why S-curves are shaped like an S
Every capital project follows the same pattern of work intensity over time. Mobilisation and early engineering ramp up slowly; peak construction produces the highest rate of work; commissioning and close-out taper off. When you plot cumulative work against time, the result is the characteristic S shape.
S-curves are used for two different measures on the same project:
- Cost S-curves — cumulative planned spend, actual spend, and (for EVM projects) earned value, all in currency units
- Physical progress S-curves — cumulative percent complete of physical work, typically cost-weighted so activities with more scope contribute more to the curve
Contract reporting usually requires both.
Building an S-curve in Primavera P6
- Resource-load the schedule — every activity gets a resource assignment with units or cost (or both). Without loading, P6 has nothing to sum.
- Open the Resource Usage Profile (View → Show on Bottom → Resource Usage Profile) or the Activity Usage Profile for activity-based cost curves
- Switch to Cumulative view in the profile options
- Filter to the WBS or activity code you want the curve for — total project, area, discipline, or work package
- Add the baseline curve as a separate series so planned vs current is visible
- Export to Excel for formal reporting if the client wants a polished chart alongside a variance narrative
The three curves that tell the story
A standard monthly S-curve chart has three cumulative series plotted against the same time axis:
- Planned / Baseline (BCWS) — what the baseline said should be spent (or completed) by each date
- Actual (ACWP) — what has actually been spent (or actually completed)
- Earned (BCWP) — the baselined value of the work that has been physically completed to date
Comparing these three tells you exactly where the project is:
| Pattern | What it means |
|---|---|
| Actual > Planned, Earned = Planned | Spending faster than budgeted, but delivering on schedule. Cost overrun without schedule benefit. |
| Actual = Planned, Earned < Planned | Spending on plan but not delivering the work. Schedule slippage; SPI < 1. |
| Actual > Planned, Earned > Planned | Spending more but also delivering more — ahead of plan on both cost and schedule. |
| Actual < Planned, Earned < Planned by same amount | Slow start — low burn AND low delivery. Neither cost nor schedule alarm yet, but ramp-up is behind. |
Cost vs physical-progress S-curves
Both curves matter; each tells you something different.
- Cost S-curve — useful for cash-flow forecasting, funding drawdown, and CFO reporting
- Physical-progress S-curve — useful for delivery status, Engineer reporting, and identifying where physical work is falling behind cost
The classic warning pattern on any EPC project is when cost S-curve is on plan or ahead, but physical-progress S-curve is behind. That means money is being spent without earning progress — the tell-tale sign of productivity problems, materials shortages, or unrecognised delay.
S-curves and early warning
The reason S-curves matter so much in weekly and monthly reporting is that deviations show up here weeks before they show up on the critical path. A cumulative curve that starts to diverge from baseline in month three is warning of a schedule impact that may not hit the critical-path finish until month six. Acting on the S-curve signal early is what separates disciplined project controls from firefighting.
S-curves and delay analysis
S-curves are not themselves delay-analysis outputs, but they are supporting evidence in every claims pack. The pattern of divergence between planned and actual physical-progress S-curves — with dates and events overlaid — is one of the clearest visual demonstrations of programme impact. For the full method: Primavera P6 delay analysis.
Refresh the cost and physical S-curves every Friday. If either has drifted more than 5% from baseline over the last four weeks, the Monday PM meeting has a new agenda item.
FAQ
Our 24-hour Primavera P6 course covers resource loading, cumulative curve setup, cost + physical progress reporting and EVM integration — with real EPC exercise files.