Cost to complete is the honest answer to "how much more will this job cost me?" It starts with the commitments you've made and haven't been billed for, then adds an estimate of everything still to buy or build: the remaining crew days, the trim material, the final cleanup. It is a judgment, updated as the job moves, not a number the software can know on its own.
A worked number
Budget $48,000. Recorded cost $31,900. Commitments outstanding $8,300. Remaining work not yet committed, estimated from the budget lines still open: $10,200. Cost to complete is $18,500, and the expected final cost is $50,400, which is $2,400 over budget with time to do something about it.
The mistake it hides
Using the budget remainder as the cost to complete. "Budget minus spent" assumes the job is tracking exactly to plan; a cost to complete built from what's actually left to do catches the overrun while it's still a conversation with the client, not a write-off.
In Obra
The project's forecast review asks you for one figure, remaining to spend, and that is where open commitments and the remaining work belong; the expected final cost is recorded cost plus that figure and never drops below what's already recorded. The job cost and profit calculator runs the same arithmetic on paper.