Scope, schedule, and cost are the three pillars of project control — tightly linked through the Work Breakdown Structure (WBS).

1. The Scope–Cost–Schedule Relationship

• Scope defines what work must be done.
• The schedule defines when it will be done.
• Cost defines how much it will take.

If one element changes, the others must be adjusted.

For example:

• Expanding scope (adding a new floor) → increases both cost and schedule.
• Accelerating schedule (faster delivery) → increases cost due to overtime or additional crews.

2. Work Breakdown Structure (WBS) Integration

The WBS links activities to budget line items.

Each work package includes:

• Defined scope of work
• Assigned resources (labor, material, equipment)
• Estimated cost and duration

3. Time-Phased Budgets

A time-phased budget (or cost-loaded schedule) distributes total cost along the project timeline.

This helps managers:

• Monitor actual vs. planned spending
• Identify early cost overruns
• Forecast monthly cash requirements

4. Earned Value Integration

Earned Value Management (EVM) links:

• Planned Value (PV) – Budgeted cost of scheduled work.
• Earned Value (EV) – Budgeted cost of completed work.
• Actual Cost (AC) – Real cost incurred.

By tracking these, the project manager can measure:

• Cost Performance Index (CPI) = EV / AC
• Schedule Performance Index (SPI) = EV / PV
  

“Cost control is not about spending less — it’s about knowing when and why you’re spending.”