Schedule Performance Index (SPI)
DE: Terminleistungsindex (SPI)
A measure of schedule efficiency: EV / PV.
Detailed Explanation
SPI measures schedule efficiency as the ratio of earned value to planned value (SPI = EV / PV). It indicates how efficiently the team is using its time relative to the plan.
SPI of 1.0 = on schedule; >1.0 = ahead of schedule; <1.0 = behind schedule. Unlike CPI which measures cost efficiency, SPI measures time efficiency. However, SPI has a known limitation: it always converges to 1.0 as the project nears completion.
SPI is used alongside CPI for comprehensive project health assessment. A project with CPI > 1.0 but SPI < 1.0 is under budget but behind schedule — possibly because the team is being too cautious. The combination tells a richer story than either metric alone.
Key Points
- Formula: SPI = EV / PV
- 1.0 = on schedule; >1.0 ahead; <1.0 behind
- Measures time efficiency relative to the plan
- Known limitation: converges to 1.0 near project end
- Used alongside CPI for complete health picture
- Part of the EVM framework
Practical Example
At month 5: PV = EUR 250K (planned work), EV = EUR 200K (work actually done). SPI = 0.80 — the project has accomplished only 80% of planned work. Combined with CPI of 0.95, the PM concludes: 'We are behind schedule but nearly on budget — we need to focus on throughput, not cost-cutting.'
Tips for Learning and Applying
Track SPI alongside CPI — neither alone is sufficient
Be aware of SPI's convergence limitation near project end
SPI < 0.80 early in the project is a serious warning sign
Use SPI trends (improving, declining, stable) for forecasting
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