Schedule Performance Index
This guideline describes how to measure Schedule Performance Index (SPI) to measure how effective you are using time.
Main Description

Overview

The Schedule Performance Index (SPI) metric is used for measure how effective you are using time in an iteration or in a project This help in identifying the trend of how are we progressing against the plan. You can use SPI for iteration plan or project plan. SPI helps the team to understand the efficiency of time spending and can adjust the future plan based on the trends recorded in previous SPI.

Measurement Method

SPI = Earned Value / Planned Value - where

Earned Value = Value of completed work items to date in terms of the budget assigned to the work item. This can be the number of earned velocity (hours, days, ideal days, points) to date.

Planned Value = Planned value of completed work items to date. This can be planned velocity (hours, days, ideal days, points) to date.


Measurement Analysis

SPI indicates that how efficiently the project team is spending the time against plan. SPI should be close to 1 as much as possible. If SPI is more than one, it indicates favorable condition which shows that the team is getting more work done than plan. If SPI is lower than 1, it indicates unfavorable condition which shows that the team is getting less work done than plan.

From the following table, at the end of week 4 (9/26/2008), the teams plan on completed 48 hours of work but they can only completed 36 hours of work. The SPI to date of this project is 0.75 (36/48). This indicates that for each 8-hour working day, only 6 hours of planned work is getting done which means only 75% of planned work being accomplished in one day. 

Dates Plan Value
(person-hours)
Earned Value
(person-hours)
09/05/2008 6
09/12/2008 20 20
09/19/2008 32  32
09/26/2008 48 36
10/3/2008 87