Schedule Performance Index (SPI)
An indicator of schedule efficiency calculated by dividing earned value (EV) by planned value (PV).
Key Points
- Formula: SPI = EV / PV; it compares authorized work accomplished to the work that was planned by this point.
- Interpretation: SPI > 1.0 means ahead of schedule, SPI = 1.0 means on schedule, SPI < 1.0 means behind schedule.
- Use only when PV > 0 and when EV and PV are measured against the same baseline; track SPI trends to monitor schedule health and forecast performance.
- SPI shows relative schedule progress, not calendar time impact; combine with critical path analysis and CPI for a fuller picture.
Example
By the end of month 3, PV is 150 units of work and EV is 120 units. SPI = 120 / 150 = 0.80. The team is progressing at 80 percent of the planned rate, indicating the project is behind schedule.
PMP Example Question
A project reports EV = 275 and PV = 250 near the end of a phase. What is the SPI and how should the project manager interpret it?
- 0.91; the project is behind schedule
- 1.10; the project is ahead of schedule
- 1.00; the project is on schedule
- 1.10; the project is over budget
Correct Answer: B — SPI of 1.10; the project is ahead of schedule
Explanation: SPI = EV / PV = 275 / 250 = 1.10. An SPI greater than 1 indicates the project is ahead of schedule; cost status is not assessed by SPI.
