Why Job Costing Matters for Contractors

A contracting business can look profitable on the Profit & Loss and still be quietly losing money on its biggest jobs. That’s not a paradox — it’s what happens when profitable small jobs subsidize unprofitable big ones and nobody can see it, because the books only track totals.

Job costing is the fix: attributing every dollar of labour, materials, subcontractors, and a fair share of overhead to the specific job that caused it.

What job costing actually tells you

With real job-level numbers, you can answer questions that totals never will:

• Which jobs made money? Not “did we make money this year” — which specific projects earned their keep, and which ones you’d have been better off declining.
• Which type of work is most profitable? Service calls vs. new builds vs. renovations often have wildly different margins. Most contractors are surprised which one wins.
• Are your estimates any good? Comparing estimated vs. actual cost per job, every job, is the only way estimating improves. Without it you keep making the same pricing mistake at full confidence.
• Where do jobs bleed? Usually it’s labour overruns and untracked change-orders — both invisible without per-job tracking.

The pieces that get missed

Labour burden. An employee’s cost isn’t their wage. CPP, EI, WSIB premiums, vacation pay, and benefits add real percentage points on top. Costing jobs at raw wage rates understates labour on every single job — which flatters exactly the labour-heavy jobs most likely to be losing money.

Overhead allocation. Trucks, insurance, shop rent, and the office don’t belong to any one job, but they have to be carried by all of them. A simple, consistent allocation (per labour-hour or as a percentage of direct costs) beats a sophisticated one nobody maintains.

Subcontractors. Sub costs need to land on the right job — and if you’re in construction and paid a subcontractor more than $500 in a year, you likely have T5018 filing obligations with CRA on top.

Work in progress. On jobs that span month-ends, costs pile up before the invoice goes out. If your books don’t account for WIP, monthly profit swings wildly and means very little.

How to start without drowning

QuickBooks Online’s projects feature handles job costing well if transactions get tagged consistently — the discipline matters more than the tool. The workable sequence:

1. Tag every invoice, bill, expense, and timesheet entry to its job as it happens (not in a heroic quarterly catch-up).
2. Cost labour at a burdened rate, not raw wages.
3. Review job profitability while jobs are running — a monthly job report catches an overrun in time to do something about it.
4. Close out every finished job with a quick estimated-vs-actual review.

If your project management software (Jobber, Procore, Buildertrend, SiteMax) doesn’t talk to your books, that’s fixable too — syncing the two so they agree is part of what we do.

We build job costing into monthly bookkeeping for contractors, and if you’d rather start DIY, our Job Costing & Project Tracker template covers steps 1–4 in a spreadsheet. Either way: stop pricing your next job with last year’s blind spots. Book a free call.