Last edited 14 Mar 2017

Schedule performance index (SPI)

The schedule performance index (SPI) is a measure of how close the project is to being completed compared to the schedule.

As a ratio it is calculated by dividing the budgeted cost of work performed, or earned value, by the planned value.

For example:

  • A project has a budgeted cost of £120,000.
  • According to the schedule, 15% of the project should have been completed after one month. That is £120,000 x 15 / 100 = £18,000.
  • But after a month, only 12% of the project has actually been completed, at a cost of £10,000.

The schedule performance index (SPI) = 10,000 / 18,000

SPI = 0.55

This means that for every estimated hour of work, the project team is completing only 0.55 hours (just over 30 minutes).

If the ratio has a value higher than 1 this indicates the project is progressing well against the schedule. If the SPI is 1, then the project is progressing exactly as planned. If the SPI is less than 1 then the project is running behind schedule.

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