What bookkeeping records
Bookkeeping captures transactions in the general ledger, reconciles bank and credit-card accounts, and produces the monthly financial statements. It answers the question 'what happened in the business as a whole?'
What job costing explains
Job costing takes those same transactions and assigns them to the customer, invoice, and job that produced or consumed them. It answers a much more specific question: 'on this job, did we make money?'
- Labor — wages, taxes, and burden
- Materials — including deposits and returns
- Subcontractors — with billing timing
- Payroll taxes and workers' comp
- Financing costs and processing fees
- Allocated overhead
Estimated versus actual
Every estimated job margin is a forecast. Every actual job margin is a reconciliation. A healthy contractor practice compares the two consistently — not only after the job is closed, but while it is still in production, so that pricing, purchasing, and change-order behavior can adjust before the damage is done.
How both systems should connect
The chart of accounts, the customer and job list, the payroll journal, and the reporting package all need to speak the same language. When they do, job reports and financial statements agree. When they don't, the numbers argue with each other and the owner ends up trusting neither.