How does a project manager use the CPI?

A project manager uses the Cost Performance Index (CPI) as a key performance metric to assess the financial efficiency of a project. By comparing the earned value (EV) of the work completed to the actual costs (AC), the CPI helps determine if the project is on budget; a CPI greater than 1 indicates good performance, while a CPI less than 1 signals cost overruns. This information guides decision-making and helps the project manager implement corrective actions as needed to keep the project on track financially.