What is the Schedule Performance Index (SPI)?
The Schedule Performance Index, commonly abbreviated as SPI, is one of the key outputs of Earned Value Management. It tells the project manager how far forward or behind the project is at the point of analysis.
“The Schedule Performance Index (SPI) is a measure of schedule efficiency, expressed as the ratio of earned value to planned value.” According to the PMBOK Guide
Schedule Performance Index ( SPI) per project is a key project management performance measure that answers the question “Is your project behind or ahead of schedule in terms of time?” This indicates how efficiently time is used to complete a project by comparing what has been done to a certain date with what should have been completed to a certain date.
Schedule Performance Index (SPI) Formula
Schedule Performance Index = (Earned Value) / (Planned Value)
SPI= EV / PV
- If SPI is less than 1, this means that the project is behind schedule.
- If SPI equal 1, this means that the project is on schedule
- If SPI is greater than 1, this means that the project is ahead of schedule.
Schedule Performance Index (SPI) Example
Project XYZ to be completed in 12 months, and the budget is 220,000 USD. Six months have passed, and 120,000 USD has been spent, but upon closer review, you find that only 40% of the work has been completed so far.
Find the Schedule Performance Index and deduce whether the project is ahead or behind of schedule.
Given in the question:
Actual Cost (AC) = 120,000 USD
Planned Value (PV) = 50% of 220,000 USD
In the question, the Planned Value(PV) is not given. However, the project duration is 12 months & 6 months have passed. In this situation, you can assume the budget was distributed equally for each month. Therefore, in 6 months, 50% of the budget will have been spent.
Earned Value (EV) = 40% of 220,000 USD
= 88,000 USD
Schedule Performance Index (SPI) = EV / PV
= 88,000 / 110,000
Hence, the Schedule Performance Index is 0.8
This means that Project XYZ is behind schedule since the Schedule Performance Index is less than 1.