Work out schedule performance index instantly with clear inputs, formula shown and shareable results.
SPI is earned value over planned value: below 1.0 means less work has been completed than planned. Projecting the finish date by inflating only the remaining duration — rather than the whole duration — is more realistic, because time already elapsed cannot be recovered.
Schedule performance index
SPI = Earned value / Planned value
Projected duration
Projected = Months elapsed + (Original duration - Months elapsed) / SPI
Because both earned and planned value converge on the total budget as work completes, so SPI loses its diagnostic power in the final stages.
Earned schedule, which expresses progress in time units directly and does not degenerate as completion approaches.