Job costing means tracking every dollar you spend against the specific project it belongs to. Instead of knowing you spent $40,000 on materials last month across all your jobs, you know exactly which project each purchase went to and whether that project is running over or under budget.

Construction businesses need this because the difference between a profitable job and a money-losing one often isn’t obvious until it’s too late. A project can look fine on the surface while quietly eating into your margins through small overruns that add up. Without job costing, you won’t see the problem until the job is done and you realize you barely broke even on what should have been a 20% margin project.

The typical setup tracks three main cost categories per project. Labor includes your crew’s hours, coded to the specific job they worked on each day. Materials cover everything you buy for that project, from lumber and concrete to fasteners and finishes. Subcontractor costs capture every invoice from the trades you hire for specialized work.

More sophisticated job costing adds cost codes or phases within each project. A general contractor building a custom home might track foundation, framing, roofing, mechanicals, and interior finish as separate phases. This lets you see that you consistently run over on framing but under on foundation, information that helps you bid more accurately on future work. A San Diego bookkeeper familiar with construction can help structure these categories to match how you actually estimate and build.

Equipment costs and overhead allocation are the tricky parts. Some contractors track equipment hours by job. Others calculate a daily or weekly equipment rate and charge it to active projects. Overhead like insurance, office rent, and administrative salaries gets allocated across jobs based on revenue, labor hours, or some other method. The allocation isn’t perfect, but it’s better than ignoring overhead entirely when calculating job profitability.

The payoff is knowing your true margins by project. You can see which types of work actually make money and which jobs looked profitable on the bid but didn’t pan out. You can identify which project managers run tighter jobs and which subcontractors hit you with extras. Your future estimates get better because they’re based on actual cost history rather than guesses.

Job costing requires discipline. Every expense needs to be coded to a job. Every timecard needs to specify which project the hours went to. The numbers are only as good as the data going in. Most construction businesses handle this through accounting software configured for construction job costing, whether that’s QuickBooks set up with projects and classes or industry-specific platforms like Buildertrend or Foundation.

For San Diego contractors wondering whether the effort is worth it, consider how you currently answer “what’s my margin on this job?” If you can’t answer that confidently for your last five completed projects, job costing fills that gap.