The Schedule Performance Index (SPI) is a key performance metric used in project management to assess how well a project is adhering to its planned schedule. It is calculated by dividing the earned value (EV) of the work completed by the planned value (PV) of the work scheduled. An SPI value of 1 indicates that the project is on schedule, while a value less than 1 suggests that the project is behind schedule. Monitoring the SPI helps project managers identify potential delays and take corrective actions. By regularly evaluating the SPI, teams can make informed decisions to keep the project on track and ensure successful completion. This metric is part of the broader framework of Earned Value Management (EVM), which integrates scope, schedule, and cost to provide a comprehensive view of project performance.