Cost Performance Index (CPI)
A measure of cost efficiency calculated as earned value divided by actual cost.
The Cost Performance Index (CPI) measures cost efficiency, calculated as CPI = Earned Value (EV) ÷ Actual Cost (AC). A CPI of 1.0 means spending exactly as planned; below 1.0 signals a cost overrun; above 1.0 means work is costing less than budgeted. On the exam, CPI forecasts the Estimate at Completion via EAC = BAC ÷ CPI, assuming current efficiency continues. Don’t confuse CPI with SPI (EV ÷ PV): AC measures money spent while PV measures planned value, so a project can be over budget (CPI < 1) yet ahead of schedule (SPI > 1).
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