Schedule Performance Index (SPI)

SPI is earned value divided by planned value. A value of 1.0 means the project is on schedule in terms of work completed; above 1.0 is ahead; below 1.0 is behind. It is a ratio, so it can be compared across projects of different sizes, unlike schedule variance, which is an absolute amount. Like schedule variance, SPI should be interpreted with care late in a project and alongside critical path analysis. Example: Earned value is 75,000 and planned value is 100,000. SPI is 0.75. For every unit of work planned, 0.75 units have been completed. SPI is useful for trend lines and for comparing projects in a portfolio. A falling SPI over several periods is an early warning even if the absolute amounts are small.