The Schedule Performance Index (SPI) in Zoho Projects is calculated as EV (Earned Value) divided by PV (Planned Value). SPI above 1.0 means the team is completing more work than planned for this point in time (ahead of schedule). SPI below 1.0 means less work is complete than planned (behind schedule).
SPI has a known limitation: as a project approaches completion, SPI always converges toward 1.0 regardless of past schedule performance, because EV and PV both approach the total budget. SPI is most meaningful in the middle phases of a project, not near the end.
Projects with SPI below 1.0 and CPI below 1.0 are the most problematic — they are both behind schedule and over budget. This combination is the most difficult to recover from and usually requires scope reduction or significant resource addition to save the schedule.
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