Accounting tells you how the business did; job costing tells you which jobs did it. The architecture is one ledger per job, with the contract, the change orders, every cost with its category and receipt, and every payment collected. A busy month hides losing jobs. Two profitable remodels can carry a third that quietly eats its margin in change-order materials nobody wrote down, and without job costing the third stays invisible until it's finished.
A worked number
Three jobs in a quarter: $71,100, $49,500 and $38,500 in revenue, $159,100 total. Direct costs $114,900 total, a 27.8% blended margin that looks fine. Per job: 29%, 34% and 12%. The third job lost most of its margin to an allowance overage and a rain week, and it's the kind of job the contractor is about to bid again at the same price.
The mistake it hides
Costing jobs from the office, after the fact. The costs reach a job through the people who spend the money, and if a foreman's receipts don't have a way in, the job's cost is whatever the office happened to see. Job costing is a capture problem first and an arithmetic problem second.
In Obra
Each project is a ledger: contract, change orders, costs with receipts, payments, budget, forecast and close. Receipts arrive by WhatsApp, email or photo and are confirmed by a person. The free job costing spreadsheet is the same model on paper, and the apps roundup compares the tools.