The Schedule Performance Index (SPI) is the ratio of work performed to work scheduled: SPI (Schedule Performance Index) = EV/ PV (if SPI < 1 means the Project is behind schedule), where PV (Planned Value): planned complete work at the time of analysis; EV (Earned Value): values accomplished at the time of analysis.

Related Definitions in the Project: The Project Management; Project Schedule; EVM (Earned Value Management)