Bookkeeping for Contractors: How Job Costing Actually Works

What Job Costing Is (and Isn’t)

Job costing is the practice of tracking income and expenses by individual project instead of lumping everything into one company-wide total. Standard bookkeeping tells you whether the business made money overall last month. Job costing tells you whether a specific job made money, which is a very different and much more useful question for a contractor bidding future work.

It isn’t the same as estimating. An estimate is a prediction made before the job starts. Job costing tracks what actually happened, so you can compare the two and get better at estimating over time.

Why It Matters More for Trades Than Almost Any Other Industry

A service business with one type of work and steady monthly billing doesn’t need job costing the way a contractor does. Construction and trades work is project based. Every job has its own materials, labor, subcontractor costs, and equipment use, and margins vary a lot job to job even within the same business. Without job costing, a contractor can be profitable on paper company-wide while actually losing money on certain types of jobs, with no way to know which ones.

The Core Components of Job Costing

Materials

Every material purchase needs to be tagged to the job it was bought for, not just recorded as a general supplies expense.

Labor

Labor costs, including payroll burden such as taxes, insurance, and benefits, need to be allocated to the jobs that labor actually worked on. This is one of the trickiest parts to track accurately, especially when crews split time across multiple jobs in a day.

Subcontractors

Subcontractor invoices should be tagged to the specific job and tracked against what was budgeted for that portion of the work.

Equipment and overhead

Equipment use and a reasonable share of overhead can be allocated to jobs too, though many contractors track this at a simpler level than materials and labor.

Setting This Up in QuickBooks Online

• Use the Projects feature, or classes and locations depending on your plan, to track each job separately
• Tag every expense, bill, and timesheet entry to the correct project as it’s entered, not after the fact
• Set up items or services that map to your actual cost categories, such as labor, materials, subs, and equipment
• Run job profitability reports regularly, not just at the end of a job

The setup matters as much as the ongoing tracking. A QuickBooks file that wasn’t built with job costing in mind usually needs real reconfiguration, not just a new habit of tagging things correctly.

What Good Job Costing Tells You

Done consistently, job costing answers questions that general bookkeeping can’t: which types of jobs are actually profitable, whether a specific crew or subcontractor is running over budget, whether your estimates are consistently too low on materials or labor, and whether a client relationship is worth continuing at the rates you’re charging.

The Common Failure Point

Job costing breaks down when tagging becomes inconsistent, usually because it’s treated as an afterthought during a busy season. A purchase gets coded to general expenses instead of the job, a timesheet doesn’t specify which project, and the resulting report is incomplete right when it would be most useful, such as at bid time or when deciding whether to take on more work. Consistency matters more than complexity here. A simple system followed every time beats a detailed system followed occasionally.

Where Bookkeeping Support Fits In

Job costing is bookkeeping work, and it’s most effective when it’s built into the regular monthly process rather than reconstructed later from memory and paper receipts. Scarlet Ibis Bookkeeping works with contractors and trades businesses on exactly this kind of setup, through bookkeeping for construction and trades, so job costs are tracked accurately as the work happens.

The Bottom Line

If you don’t know which of your jobs actually make money, job costing is the fix, and it starts with tagging every cost to the right project consistently, not with complicated software. Get the tracking habit right and the reports that matter will follow.