An SPI of 0.8 means that the project is:

• A. 50% behind schedule
• B. 20% behind schedule
• C. 80% complete
• D. Ahead of schedule

Answer: (B)

Schedule Performance Index measures how efficiently the project is progressing against the plan by comparing the value of work actually performed to the value of work planned. It’s calculated as EV divided by PV. If SPI is less than 1, you’re behind schedule; if it’s greater than 1, you’re ahead; if it equals 1, you’re on schedule. An SPI of 0.8 means you’ve earned value equal to 80% of what was planned by this point, so about 20% of the planned progress is missing. That’s why the project is behind schedule by 20%. The other interpretations don’t fit: 50% behind would require an SPI around 0.5, 80% complete isn’t a direct read on schedule efficiency, and ahead of schedule would need an SPI above 1.