A schedule performance index (SPI) is an efficiency metric of how far ahead, behind or on time you are on a project. Put simply, it measures how on-pace you are to meet a project timeline. It’s calculated based on your project’s planned value (PV) and earned value (EV) using the estimate determined at the project’s start. Show SPI is one of several numeric values that form your construction project’s overall earned value management, a method that tracks and forecasts the ongoing schedule and cost performance of your build. So how do you arrive at this metric and what exactly does it tell you? Determining an SPICalculating a schedule performance index requires one simple equation: SPI = EV/PV You’ll need the budget at completion (BAC), also referred to as budgeted value, from your estimate that was created at the beginning of the build. Accuracy is key here; if anything is too far “off” you could end up with a skewed SPI that tells you a different story about how well your project is actually meeting schedule milestones.
PV = % complete (planned) x Budget at Completion (BAC)
EV = % complete (actual) x Budget at Completion (BAC) Let’s look at an example using numbers for better context. Say you have a six-month project with a BAC of $1,000,000. If you want to know what the value of the work done after two months should be, you would calculate it as follows: PV = % complete (2 months/6 months) x $1,000,000 PV = 33% x $1,000,000 PV = $333,333 To track the work that was actually done when you hit that two-month mark, you’ll calculate the EV. In our scenario, let’s say 60% of the work was done. The equation would be: EV = 60% x $1,000,000 EV = $600,000 From there, you can determine your project’s timeline efficiency — your SPI: SPI = EV/PV SPI = $600,000/$333,333 SPI = 1.8 What do SPI values mean?
Referring to the example above, because the SPI of 1.8 is greater than 1, the project appears to be ahead of schedule. Individually, these values provide a snapshot of what current work performance looks like. You can track them over time to see if there are any trends across the overall project or within specific phases. However, it’s a good idea to assess SPI in tandem with other metric methods. Why? If another measurement doesn’t align with what the SPI shows, you will have the opportunity to dive into the numbers to see if there’s more going on below the surface that you wouldn’t have known about otherwise. Why is knowing your SPI important?Of course, being ahead of schedule or on time are the ideal scenarios. But we all know timelines are at the mercy of so many variables: weather, supply chain disruptions, natural disasters or late-arriving materials. When you see your schedule performance index dip below 1, consider it an alert that gives you a chance to avoid or minimize the possible consequences that being behind can bring, such as:
Calculating your project’s schedule performance index is technically easy. But when you’re managing large capital builds or public works projects, the calculations really add up. InEight’s estimating software can automate this process for you so you know how well each phase of your project is performing against established timelines. InEight’s data analytics software gives you visibility into your performance numbers, so you can pinpoint issues as they occur and have more control over how to address them. You’ll be able to make more timely decisions if schedules start to deviate, reducing the likelihood of you being caught off guard. What do you do when SPI is less than 1?SPI = EV / PV
If the SPI calculation yields a value that is: Greater than 1: The project is ahead of schedule. Less than 1: The project is behind schedule.
What does a SPI value of 1 min?And, if your SPI is equal to 1, your project is exactly on schedule. In summary: SPI > 1: Project is ahead of schedule; more work has been completed than expected. SPI < 1: Project is behind schedule; less work has been done than planned.
What does the schedule Performance Index SPI say about the project?The schedule performance index (SPI) is a measure of the conformance of actual progress (earned value) to the planned progress: SPI = EV / PV. In both of the above formulas, a value of 1.0 indicates that the project performance is on target.
What does SPI greater than 1 mean?SPI = Earned Value / Planned Value. If CPI is less than 1 then project is over budget. If SPI is less than 1 then project is behind schedule. If CPI is greater than 1 then project is under budget. If SPI is greater than 1 then project is ahead of schedule.
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