EAC — if schedule variance continues
This is another version of EAC, the "Estimate at Completion," which is your updated forecast of the project's total final cost. Here the forecast is driven by how the project is performing on SCHEDULE rather than on cost. The idea is that falling behind (or getting ahead of) schedule can carry a cost impact, and this formula estimates that.
The formula is EAC = BAC / SPI. BAC is the "Budget at Completion," your original total planned budget. SPI stands for "Schedule Performance Index," a number that shows how efficiently you are progressing through the work compared to the plan. An SPI of 1.0 means you are exactly on schedule, below 1.0 means you are behind schedule, and above 1.0 means you are ahead of schedule.
To use it, divide your original budget (BAC) by your current SPI. If the result is higher than BAC, the schedule slippage is expected to push your costs up; if it is lower, being ahead of schedule points toward savings. A project manager chooses this version when the main worry is that schedule delays — not pure spending inefficiency — are the force expected to keep shaping the final cost.
Think of it like paying a crew by the day to build a fence. If they're only finishing 90% of the work each day that they promised, the job stretches out longer than planned — and every extra day of labor quietly adds to the final bill.
Suppose your project's total planned budget (BAC) is $100,000. You check your Schedule Performance Index (SPI) and find it is 0.90, meaning you have completed only 90% of the work you had planned to finish by now — you are running behind. You calculate EAC = BAC / SPI = $100,000 / 0.90 = $111,111. This suggests that if the schedule keeps slipping at this rate, the extra time will drive the total cost up to about $111,111, roughly $11,000 over the original budget.
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