Job Costing for Contractors

What job costing actually is — and what it isn't

Job costing is the practice of allocating every dollar of cost — labor, materials, equipment, subcontractors, overhead — to the specific job that consumed it. The output is one number per job: gross margin. The input is a process most contractors never finish setting up.

Most contractors think they have job costing because their FSM tracks job revenue. They don't. Revenue is half the equation. Without cost allocation tied to the same job, you have a revenue ledger and a payroll ledger, but no margin.

The 91% problem: most jobs have no cost data attached

Across 2,200+ contractors and 3.84M jobs in our dataset, 91% of jobs have revenue logged but no labor, material, or subcontractor cost coded to the same job. The costs exist — they're in payroll runs and AP invoices — but they're not allocated.

This is the silent killer of contractor profitability. Profitable jobs subsidize unprofitable ones, the owner sees a healthy company-level P&L, and individual losers stay invisible until cash gets tight.

The fix starts with operational discipline — every timesheet codes to a job, every PO references a job, every receipt gets allocated — but it requires accounting to mirror the field. Most contractors stop at one of those two halves.

What good looks like: percentile benchmarks

Among the 9% of jobs that DO have cost data attached, gross margins distribute normally between 20% and 50% — exactly what CFMA benchmarks predict for the trades. By trade we see medians around 38% gross margin for HVAC, plumbing, and mechanical, with electrical slightly lower at ~35% and roofing closer to 30%.

Top quartile contractors run 50%+ gross margins on a blended book. Bottom quartile sits below 20% and often doesn't realize it because the company-level P&L looks fine.

The spread between bottom and top decile is 100 points across our sample. That spread is what cost visibility unlocks — not pricing alone, but the ability to see which jobs are killing you and re-bid them.

The small-jobs trap: where margin blindness compounds

1% of jobs (in the 80–200 hour range) generate 49% of revenue across our dataset. The other 99% — 767K service calls under 4 hours — generate just 8% of revenue but consume more than half the operational complexity.

Most cost tracking discipline gets applied to the big jobs. The small ones get bucketed, billed, and forgotten. If even 20% of those small jobs run at a loss, that's $140M in revenue subsidizing losses across the dataset — and nobody can see it.

The fix isn't to chase a perfect time sheet on every $200 service call. It's to use job-type averages from the jobs you DO track to flag the ones that look out of pattern. A $300 job that took 6 hours and used $150 in parts isn't profitable — but it'll never get flagged unless you're building the average and comparing.

Fixing the process: the 90-day playbook

• Audit your last 90 days of completed jobs. Pull every job with revenue and check whether labor cost, material cost, and subcontractor cost are coded to that job. Compute the percentage. If it's under 80%, the problem is operational, not accounting.
• Set a rule: every timesheet codes to a job, every PO references a job, every credit-card receipt gets allocated within 7 days. No exceptions. The exceptions are where margin disappears.
• Pick a job-type taxonomy you can actually maintain. Five categories beat fifty. PM, callback, install, T&M project, change order is enough for most service contractors.
• Build the weekly report: every job completed last week with revenue, cost, and margin. Sort by margin descending. The bottom 10% is your re-bid list, your scope-creep list, or your customer-fire list.
• Reconcile monthly. The job-level P&L should sum to the company P&L within rounding. If it doesn't, something is unallocated and your numbers are wrong.

When DIY stops working

Job costing is the kind of problem where the cost of getting it wrong scales with revenue. A $1M contractor with broken job costing has $50–$100K of margin hidden somewhere. A $20M contractor with the same broken process has $1–$2M in compounded blind spots and probably can't sell the business at a fair multiple.

If you've tried to fix this internally twice and it didn't stick, the issue isn't your team — it's that the gap between operations and accounting needs someone whose job is to bridge them. That's what a real CFO accelerated by AI is for.