The estimate at completion is the one number a contractor should be able to say about any open job: "this one is going to cost about $50,400." It is recorded cost plus cost to complete, and it moves every time a receipt is confirmed, a commitment is signed, or the remaining work is re-estimated. Set against the contract plus change orders, it gives the expected margin, and that is the figure that decides whether to push for a change order, hold a discount, or let a sub's invoice sit.
A worked number
Contract $68,000 plus $3,100 in change orders. Recorded cost $31,900, commitments $8,300, remaining work $10,200: estimate at completion $50,400. Expected margin $20,700, or 29% of the adjusted contract. If the cabinets come in $1,500 over, the estimate becomes $51,900 the day the invoice is confirmed, and the margin is 27%.
The mistake it hides
An estimate that can drop below what's already been spent. Some spreadsheets compute it as budget minus a percentage complete, which can produce a "forecast" lower than the receipts in hand. A forecast is only honest if its floor is the recorded cost.
In Obra
Every project shows an expected final cost built from recorded cost plus the remaining to spend you enter in a forecast review, where open commitments belong, with the recorded cost as its floor. The Help Center's glossary of Obra's own terms names the exact fields.