Cost Variance Analysis in Project Management
Cost Variance (CV) is one of the two foundational variance metrics in Earned Value Management (the other being Schedule Variance). It measures the difference between the budgeted value of work completed and the actual cost of completing that work. Put simply: are we spending more or less than we should for the work we've done?
The Cost Variance Formula
Where:
- EV (Earned Value) = the budgeted value of work actually completed (% complete × BAC)
- AC (Actual Cost) = the actual money spent to complete that work
How to Interpret CV
| CV Value | Meaning | Action |
|---|---|---|
| Positive (+) | Under budget — delivering value cheaper than planned | Investigate why (could be genuine efficiency or corner-cutting) |
| Zero (0) | Exactly on budget for work done | Continue monitoring |
| Negative (−) | Over budget — cost overrun for work completed | Root cause analysis and corrective action required |
Important: CV is measured in the same units as your budget (dollars, euros, etc.). A CV of −$50,000 is an absolute number. To understand the relative severity, calculate CV% = CV ÷ EV × 100. A −$50,000 CV on a $5M project (−1%) is very different from the same CV on a $500K project (−10%).
CV vs. CPI: What's the Difference?
CV and CPI both measure cost performance but in different forms:
- CV = EV − AC: an absolute dollar amount. Shows the magnitude of the variance.
- CPI = EV ÷ AC: a ratio/index. Shows the rate of cost efficiency. Better for comparing projects of different sizes.
Both CV and CPI are driven by the same underlying data. If CV is negative, CPI will be < 1.0. If CV is positive, CPI will be > 1.0.
Worked Example
A bridge construction project: BAC = $3,000,000. At month 8:
- EV = $1,200,000 (40% complete × $3M)
- AC = $1,450,000 (actual spending to date)
CV% = CV ÷ EV × 100 = −250,000 ÷ 1,200,000 × 100 = −20.8%
CPI = EV ÷ AC = 1,200,000 ÷ 1,450,000 = 0.828
The project is running 20.8% over budget for the work completed. For every $1.00 budgeted, it's actually costing $1.21. If this continues, EAC = 3,000,000 ÷ 0.828 = $3,623,188.
Root Cause Analysis for Negative CV
When CV is significantly negative, the project manager should conduct a Variance Analysis. Common root causes:
| Root Cause Category | Examples |
|---|---|
| Scope creep | Undocumented scope additions consuming budget without BAC increase |
| Estimation errors | Original estimates were too optimistic |
| Resource productivity | Lower-than-expected labor productivity |
| Material costs | Price inflation, supplier changes, waste/rework |
| Risk events | Identified risks materialized without adequate contingency |
| Technical complexity | Design issues requiring additional engineering hours |
Corrective Actions for Cost Overruns
- Scope reduction: Remove or defer lower-priority deliverables to bring EAC back in line with BAC
- Resource optimization: Replace expensive resources with lower-cost alternatives for remaining work
- Process improvement: Identify and eliminate rework cycles and inefficiencies
- Risk response acceleration: Implement outstanding risk responses before they consume more budget
- Baseline revision: If CV is structural (not correctable), request formal BAC revision with sponsor approval
Variance at Completion (VAC)
CV tells you the current cost variance. VAC projects this to the end of the project:
A negative VAC means the project is projected to finish over budget. VAC provides the budget impact number that sponsors and financial controllers care most about.
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