What is SPI (schedule performance index)?

    The schedule performance index compares the value of work completed with the value planned. Below 1.0 means less work has been done than planned.

    Also written as SPI

    SPI measures progress in dollars, not time. It says nothing about which activities are late, and late work off the critical path can look the same as late work on it.

    Near the end of a project SPI drifts back towards 1.0 even when the finish date has slipped, because eventually all planned value is earned. Check float and the critical path alongside it.

    Formula

    SPI = EV ÷ PV

    Worked example

    A project has a $12 million budget (BAC). At the reporting date, $5.2 million of work was planned (PV), $4.8 million has been earned (EV) and $4.55 million has been spent (AC). SPI = 4.8 ÷ 5.2 = 0.92: about 92% of the planned work has been done.

    Related terms

    Cost performance index

    CPI

    Shows how much value of work is earned for each dollar spent.

    Formula and example

    Schedule variance

    SV

    The difference between the value of work completed and the value planned.

    Formula and example

    Critical path

    The longest chain of dependent activities through a schedule.

    Float

    How long an activity can be delayed without delaying something else.

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