Cost Performance Index Calculator
Determine how efficiently your project is spending its budget with the Cost Performance Index. Use CPI during project execution to identify cost overruns and forecast the final cost at completion.
About this calculator
The Cost Performance Index (CPI) is a core Earned Value Management (EVM) metric that quantifies budget efficiency on a project. The formula is CPI = Earned Value (EV) / Actual Cost (AC). Earned Value represents the budgeted value of work completed, while Actual Cost is what was actually spent to accomplish that work. A CPI of 1.0 means every dollar spent produced exactly one dollar of planned value — the project is on budget. A CPI below 1.0 indicates cost overrun; for instance, CPI = 0.85 means you are spending $1.00 to get only $0.85 of value. A CPI above 1.0 means the project is under budget. CPI is also used in forecasting formulas such as Estimate at Completion (EAC = Budget at Completion / CPI), making it one of the most powerful predictive tools in project management.
How to use
Imagine a software project where the team has completed work valued at $120,000 (Earned Value = $120,000), but has actually spent $150,000 to do it (Actual Cost = $150,000). Apply the formula: CPI = EV / AC = $120,000 / $150,000 = 0.80. A CPI of 0.80 means the project is getting only 80 cents of value for every dollar spent — a 20% cost overrun. If the total project budget is $500,000, you can forecast the Estimate at Completion as EAC = $500,000 / 0.80 = $625,000.
Frequently asked questions
What does a Cost Performance Index of less than 1 indicate?
A CPI below 1.0 means the project is over budget — you are spending more money than the value of work being delivered. For example, a CPI of 0.90 means that for every $1.00 spent, only $0.90 of planned value has been produced. This signals inefficiency, whether due to underestimated costs, scope creep, or resource issues. Project managers should investigate root causes immediately and consider replanning, descoping, or requesting additional funding.
How do I use CPI to forecast the total project cost at completion?
Once you have calculated CPI, you can estimate the final project cost using the Estimate at Completion (EAC) formula: EAC = Budget at Completion (BAC) / CPI. If your total budget is $200,000 and your current CPI is 0.80, the forecasted final cost is $200,000 / 0.80 = $250,000. This assumes future work will be performed at the same efficiency rate as work completed to date. This forecast should be reviewed alongside schedule performance to give stakeholders a realistic picture of project outcomes.
What is a good CPI value to aim for in project management?
A CPI of exactly 1.0 is the ideal target, meaning the project is delivering precisely the planned value for the money spent. In practice, most organizations consider a CPI between 0.95 and 1.10 to be acceptable, reflecting minor variances within normal tolerance. A CPI consistently below 0.90 is a red flag that typically requires formal corrective action or a revised baseline. Research by the US Department of Defense has shown that once CPI drops below 0.80, projects rarely recover without significant scope or budget changes.