Variance at Completion (VAC)
Variance at Completion (VAC) is the forecast gap between the approved budget and the forecast final cost: VAC = BAC - EAC. Positive means a forecast saving; negative means a forecast overrun.
Where Cost Variance reports the overspend already incurred, Variance at Completion projects the position at the finish line: the Budget at Completion minus the Estimate at Completion. With a BAC of 1,000,000 and an EAC of 1,111,111 (BAC / CPI at 0.90), VAC is -111,111 - an 11% forecast overrun, stated while there is still time to do something about it.
VAC inherits its credibility entirely from the EAC behind it. An EAC built on CPI assumes current efficiency continues; a bottom-up EAC reflects a fresh look at the remaining work. Quoting VAC without saying which forecast produced it invites false precision.
Its sign convention matches the EVM family: positive is good. Commercially, a reliable negative VAC per WBS branch is the early case for action - re-sequencing, re-resourcing, a claim, or a hard conversation - months before the overrun is a fact in the accounts.
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