Schedule Performance Index: Definition & Examples

Instructor: Lolita Jackmon

President of a local chapter of the Project Mangement Institute (PMI) and a certified Project Management Professional since 2009.

In this lesson, we will gain an understanding of what schedule performance index is, how it is used to monitor a project schedule, and how to calculate it.

Schedule Performance Index Rationale

Projects have a discrete beginning and end. The ability to monitor whether a project is on track to deliver by the desired end date, requires the use of a detailed schedule that lays out the specific tasks that will need to be completed and when they need to be complete. Schedule Performance Index (SPI) is a mathematical calculation to determine how efficient the schedule is being completed. A well-defined schedule will include task dependencies to indicate tasks that may require a predecessor task be completed before the successor task can start.

Let's consider this example. On a software development project following a waterfall approach, typically the requirements are documented before the design can begin and development usually is complete before testing starts. These tasks must finish before the software is made available to the end user.

Schedule Monitoring

To monitor if the project will meet its scheduled target dates, we should measure periodically from a specific point in time. The initial point in time is called the baseline schedule and the dates reflect when tasks should start and end to meet the goals of the project. For the purposes of Schedule Performance Index (SPI) the baseline is referred to as the Budgeted Cost of Work Scheduled or BCWS. To determine BCWS, the schedule must be structured to reflect the estimated cost of each planned task.

As the project progresses, periodic updates to the schedule are made to show progress towards completing the tasks. This is typically done using a percentage of completion between zero and one-hundred. The percentage complete is used to determine the Budgeted Cost of Work Performed or BCWP.

SPI Calculation

With the BCWS and BCWP we can calculate Schedule Performance Index (SPI). SPI is the mathematical calculation of dividing the BCWP by BCWS (BCWP/BCWS) to determine schedule efficiency. A resulting number of 1.0 indicates the project is performing as scheduled. A number greater than 1.0 indicates a project is ahead of schedule and a result under 1.0 indicates the project is behind schedule.

SPI Example

Let's look at an example calculation. Starting with the baseline (BCWS) we can calculate the work completion (BCWP) by multiplying BCWS by the percent complete. Once we have those two data points, we can add the BCWS of all activities completed or in progress and divide it by the total of the work that is completed (BCWP).

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