Schedule Performance Index Calculator

Work out schedule performance index instantly with clear inputs, formula shown and shareable results.

About Schedule Performance Index Calculator

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.

Formulas

Schedule performance index

SPI = Earned value / Planned value

Projected duration

Projected = Months elapsed + (Original duration - Months elapsed) / SPI

Worked example

With the default values below, Schedule Performance Index Calculator returns Schedule performance index of 0.8400. Change any input above and every figure here is recalculated in your browser.

Inputs used

Earned value: 10,080,000
Planned value: 12,000,000
Original duration: 18
Months elapsed: 9

Results

Schedule performance index: 0.8400
Projected duration: 19.7
Projected slippage: 1.7
Schedule variance: -$1,920,000.00

Step by step

1Values used
2Schedule performance index
3Projected duration
4Schedule performance index= 0.8400
5Projected duration= 19.7
6Projected slippage= 1.7
7Schedule variance= -1,920,000.00

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does SPI approach 1.0 near the end?

Because both earned and planned value converge on the total budget as work completes, so SPI loses its diagnostic power in the final stages.

What is a better late-stage measure?

Earned schedule, which expresses progress in time units directly and does not degenerate as completion approaches.