Schedule Performance Index (SPI)
A measure of schedule efficiency calculated as earned value divided by planned value.
Schedule Performance Index (SPI) is an Earned Value Management metric that quantifies schedule efficiency using the formula SPI = EV ÷ PV, where EV is Earned Value and PV is Planned Value. A result of 1.0 means the project is exactly on schedule; below 1.0 signals schedule slippage, and above 1.0 means the team is ahead of plan. The key exam distinction is between SPI and CPI (Cost Performance Index). Both use EV in the numerator, but CPI divides by AC (Actual Cost) to measure cost efficiency, while SPI divides by PV to measure time efficiency. A project can have a healthy CPI yet a poor SPI, so always evaluate both together.
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