Cost-to-Complete
A forecast of how much money is still needed to finish a project's remaining work, based on everything already spent and committed so far, used to determine whether the budget that's left actually covers what remains, rather than assuming the original bid will simply hold true.
Why it matters
A project can look fine by committed and actual cost alone and still be headed for a loss if the remaining work will genuinely cost more than what's left in the budget to cover it. Cost-to-complete forecasting is what actually catches that gap while there's still time to act on it, instead of discovering it only once the project is finished and the money is already spent.
On a real project
A project is 60% through its schedule with 55% of its original budget spent or committed so far, which sounds close to on-track, until a cost-to-complete forecast shows the remaining 40% of the work will actually cost closer to 50% of the total budget, because productivity on the trades still ahead has been running worse than originally estimated.
Who this matters most to
A Cost Engineer builds and updates the cost-to-complete forecast regularly throughout construction, comparing it against remaining budget to flag a developing overage early. A Project Manager uses that forecast to decide whether corrective action, re-sequencing work, renegotiating a scope, drawing on contingency, is actually needed before the project finishes.
Where this goes wrong
A project team only reconciles cost-to-complete once, at closeout, rather than updating it regularly through construction. By the time anyone actually calculates what finishing the remaining work will cost, the project is already done, the money is already spent, and there's no longer any way to correct course.