Most contractors can tell you what's in the bank account. Far fewer can tell you which job put it there — or which job quietly lost money. That gap is exactly what job costing is built to close.
What job costing actually is
Job costing means tracking the income and expenses for each job or project separately, instead of lumping everything into one general pool of "business income" and "business expenses." Materials, labor, subcontractor payments, permits, and equipment costs all get tagged to the specific job they belong to.
Why your bank balance can lie to you
A healthy bank balance can hide a job that's actually losing money, especially when a profitable job's deposit lands in the same account around the same time. Without job-level detail, it's easy to keep bidding and running jobs the same way — including the unprofitable ones — simply because nothing in the books flags the problem.
What job costing tells you that a bank balance can't
- Which types of jobs are consistently your most profitable
- Whether a specific job ran over on materials, labor, or subcontractor costs — and by how much
- Whether your bids are actually pricing in your real costs
- How retainage held back on a project is affecting your cash flow until it's released
Setting it up doesn't have to be complicated
In QuickBooks, this usually means using "classes" or "projects" to tag every transaction to a job as it's entered, plus a chart of accounts that separates materials, labor, subcontractors, and overhead. The setup work happens once; after that, it's a matter of tagging transactions consistently every month — which is exactly the kind of recurring detail that's easy to let slip when you're also running the jobs themselves.
Where retainage and subcontractor tracking fit in
Retainage — the percentage of a payment held back until a project wraps up — needs to be tracked separately so it doesn't get confused with lost revenue. Subcontractor payments need their own clean records too, both for your own job costing and to keep your 1099 documentation organized at year-end.
The bottom line
Job costing turns "the business made money this year" into "these three types of jobs made money, and this one didn't — here's why." That's the level of detail that actually changes what you bid, what you take on, and what you walk away from. It's also one of the first things we set up when we start monthly bookkeeping for a contractor.