The Schedule Performance Index (SPI) is a project management metric that measures the efficiency of a project schedule. SPI is used to determine how well a project is progressing according to the planned schedule. The SPI is calculated by dividing the earned value (EV) by the planned value (PV).
The formula for calculating SPI is:
SPI = Earned Value (EV) / Planned Value (PV)
where EV is the value of the work that has been completed up to a certain point in time, and PV is the value of the work that was planned to be completed up to that same point in time.
For example, if a project is planned to take 10 weeks to complete and is expected to cost $100,000, with a planned value of $10,000 per week, and at the end of week 5, the project has only completed $30,000 worth of work, then the EV would be $30,000, and the PV would be $50,000 (5 weeks x $10,000 per week). The SPI would be:
SPI = $30,000 / $50,000 = 0.6
This would indicate that the project is running behind schedule and is only 60% efficient in terms of schedule performance. A value of less than 1 indicates that the project is behind schedule, while a value of greater than 1 indicates that the project is ahead of schedule. A value of 1 indicates that the project is on schedule.
