How do you calculate Schedule Performance Index (SPI)?

SPI = Earned Value (EV) ÷ Planned Value (PV).

What does SPI lower than 1.0 mean?

SPI < 1.0 means the project is behind schedule based on the planned work vs completed work.

SPI shows how efficiently you’re using time against the plan. SPI below 1.0 means the project is behind schedule.

EV (Earned Value) $ PV (Planned Value) $

SPI = EV ÷ PV • SPI > 1.0 → ahead of schedule • SPI < 1.0 → behind schedule