Job Costing Example: A Real $42,000 Bathroom Remodel
Chris Sibley ·
Most job costing examples are made up — clean numbers, tidy categories, nobody forgets anything. Here's a real one instead: mine. It's the job that made me build a job costing app, and the math is worth walking through because some version of it is probably happening to you.
The job on paper
Fort Worth, 2024. Full bathroom remodel, contract price $42,000. The bid was built for roughly a 30% margin — on $42,000, that's about $12,600 staying with the company after the job's direct costs. Labor, tile, fixtures, plumbing sub, glass — all budgeted. I've done a lot of bathrooms; the bid wasn't the problem.
The job in real life
The work went fine. The client was happy. I felt like it hit the number. Three months later my accountant ran the actuals: 12% margin — right around $5,000, not $12,600. The gap was $7,500 in receipts that never made it into the job's costs when I was bidding and tracking: lumber runs, fixtures, two Home Depot trips I covered out of pocket and mentally filed under "small stuff."
Nothing dramatic went wrong. That's what makes it dangerous. No blown budget line, no bad sub — just dozens of small, unlogged costs, each too minor to remember, adding up to 18 points of margin.
The lesson in the math
- Contract price: $42,000
- Expected margin: 30% ≈ $12,600
- Actual margin: 12% ≈ $5,000
- The difference: $7,500 of uncaptured costs
Divide $7,500 by a typical receipt and you get the real villain: it wasn't one big miss, it was many small ones. A $60 fitting run here, a $140 fixture swap there, week after week. Each invisible alone. Lethal together. This is why job costing lives or dies on capture, not math.
What I changed
Every cost now gets captured the moment it exists — receipt snapped in the parking lot, AI reads it and files it to the job, voice log for the no-receipt stuff. The running margin sits on my phone, so a job trending under bid shows up in week two, not at the accountant's office in month three. I built Job Cost Proto do exactly this because I couldn't find a tool that made capture effortless enough to survive a real job week.
It's free on the App Store — 3 projects, 50 receipts a month, no credit card. Run your next job through it and find out what your 30% really is.