Schedule Performance Index (SPI): Definition, SPI Formula, Examples & Calculations

Definition: Schedule Performance Index (SPI) is the ratio of Earned Value and Planned Value and provides cost efficiency of the project.

The term “Schedule Performance Index” is popularized by the PMI. As per the PMBOK Guide, “The Schedule Performance Index (SPI) is a measure of schedule efficiency, expressed as the ratio of earned value to planned value.”

The Schedule Performance Index is a part of earned value analysis.

Schedule Performance Index (SPI) Formula

The formula to calculate SPI is given below:

Schedule Performance Index = Earned Value (EV) / Planned Value (PV)

The earned value is the value of complete work.

Planned value is the value of work that you should have earned according to the plan. 

If the SPI exceeds one, the project is ahead of schedule and performing well. Conversely, an SPI value of less than one shows the project is behind schedule and needs corrective actions to bring the project on track. An SPI value of one shows the project is on schedule.

Schedule Performance Index (SPI) Examples with Calculations

Example-1

For a project, the earned value is 20,000, and the planned value is 23,000 USD. Calculate the cost performance index.

SPI = EV/PV

= 20,000/23,000

= 0.87

Since the SPI is less than one, the project is behind schedule.

Example-2

For a project, the earned value is 23,000, and the planned value is 20,000 USD. Calculate the cost performance index.

CPI = EV/AC

= 23,000/20,000

= 1.15

Since the SPI is greater than one, you are ahead of schedule.

Summary

Schedule Performance (SPI) shows if the project is ahead or behind schedule. If the variance exceeds acceptable limits, the project manager will find the reasons for this fluctuation and take corrective actions to bring the project on schedule. 

This formula and calculation are important from a PMP exam point of view. In the PMP exam, a few questions ask for schedule performance index calculation.