Hidden Job Costing Mistakes Manufacturing Owners Make
Hidden job costing mistakes that cut manufacturing margins: setup time, machine hours, payroll burden, rework and outside processing, with a worked example.
Nauman Poonja, CPA · Updated · 9 min read · Editorial standards 
A job can ship on time, get paid in full, and still lose money. The quote looked fine. The problem is the cost side of the quote left things out.
These are the misses I would check first in any shop's job costs. None of them are exotic. They are costs the business is already paying for, they just never land on the job. Below is what they are, how to spot them, and an illustrative job that shows how fast they add up.
If you don't have a job costing system yet, start with how to set up a job costing system for manufacturers. This post assumes you have one and want to know what it's missing.
Why does inaccurate job costing hurt so much?
Because it hides. Your P&L adds up every cost in the business, so the total is right. What's wrong is which jobs carry which costs.
When the job sheet leaves out real costs, every job looks a little better than it is. You quote off those numbers. The work you're cheapest on tends to be the work that quietly eats the most hidden cost, so that's the work you win more of.
So the risk isn't one bad job. It's a quoting system that keeps steering you toward the wrong work. You end the year busy, with thin margin, and no single job to blame.
The fix starts with a list. Here is mine, roughly in the order I check them.
Mistake 1: Costing labor at the wage instead of the loaded rate
A machinist who makes $28 an hour does not cost you $28 an hour. On top of the wage you pay the employer share of payroll taxes, workers' comp, health insurance, 401(k) match, and paid time off.
If the job sheet uses the bare wage, every labor hour on every job is understated. That one setting can move a whole year of quotes.
The loaded figure is often called the burden rate. Work it out from your own payroll records, per person or per department. The percentage depends on your benefits, your state and your comp class, so I won't give you a rule of thumb. Our post on the fully loaded cost of a manufacturing employee walks through the pieces.
Mistake 2: Leaving out machine time
Material and labor usually make it onto the job. Machine hours are easier to skip. On a CNC floor or a press line, that's a big gap.
A machine has real costs whether or not anyone is standing next to it: depreciation, maintenance, tooling, power, and floor space. One operator running two machines is the obvious case. If you only cost the operator's hours, the second machine is free on paper.
Depreciation isn't cash, but it is a real cost of using the asset. The simple approach is a machine hour rate. Add up the yearly cost of the machine, divide by the hours you expect it to actually run, and charge that rate to each job for its run time.
Use realistic hours. If you divide by every hour in the year, the rate comes out too low. If you divide by what it ran in a slow year, the rate comes out too high and you lose bids. I think a normal year's run hours is the right base.
Mistake 3: Not counting setup and changeover
Run time gets tracked. Setup time often doesn't. Pulling material, loading programs, fixturing, first-article inspection, and teardown are all real hours.
On a long production run, setup is spread over thousands of parts and barely matters. On a 20-piece job, setup can be most of the labor. If you quote only run time, you're underpricing exactly the short, high-mix jobs that need the most care.
The fix is a separate setup line on the job sheet and a separate time code on the floor. Then quote setup as its own charge, or at least make sure it's in the price. If you run a lot of high-mix work, our post on high-mix, low-volume production covers the pricing side.
Mistake 4: Hiding scrap and rework in overhead
When a part gets scrapped and remade, the second round of material and labor belongs to that job. In a lot of systems it goes into a general shop labor bucket or a scrap account instead.
That makes the job look better than it was. Worse, the estimator never sees it, so the next quote for the same part makes the same assumption.
Two simple habits help. Charge rework hours to the job that caused them. And keep a scrap rate by part family or material, from your own history, so the quote includes a realistic allowance instead of assuming every cut is perfect.
Mistake 5: Dropping outside processing, freight and programming
These are direct costs that tend to get coded to a general account because the bill shows up late or nobody puts a job number on it.
- Outside processing: plating, anodizing, heat treat, powder coat, testing.
- Freight in on job-specific material, and freight out if you don't bill it.
- Programming and engineering hours spent on a specific job.
- Special tooling or fixtures bought for one customer's part.
The fix is boring and it works: every purchase order for job-specific items carries a job number, and AP doesn't enter a bill without it. Can your current system enforce that? If not, that's worth fixing before anything fancier.
Mistake 6: Indirect labor that never reaches the job
Your supervisor, quality inspector, material handler and shipping person don't make parts. Their wages are still part of what it costs to make parts.
These costs belong in overhead, and overhead has to be applied to jobs at a rate. The mistake is either not applying overhead at all, or using a rate that hasn't been updated since you added two people. Our guide to calculating labor and overhead cost shows how to build the rate.
A related problem: one plantwide rate for very different work. If a job needs three quality holds and a full inspection report, it's using more of your quality department than a simple repeat job. If both get the same rate, one is overcosted and the other is undercosted. You don't need a complicated system to fix this. Sometimes two rates, one for machining and one for assembly, is enough.
Mistake 7: Material at old cost and inventory sitting on the floor
If the job sheet pulls material at what you paid six months ago, and you have to restock at today's price, the job is undercosted by the difference. That matters more when metal prices move.
Material you buy early and hold also has a cost: the cash tied up, the space, the handling, and the risk it never gets used. I don't think you need to charge carrying cost to every job. But for jobs where you buy material well ahead for one customer, it belongs in the quote. Our post on inventory carrying costs covers how to think about it.
What do these mistakes look like on one job?
Here is an illustrative example. The numbers are made up, but the math is real. A shop quotes a machined part job at $10,000.
The job sheet as it was quoted:
| Cost line | How it was figured | Amount |
|---|---|---|
| Material | From the purchase order | $3,800 |
| Labor | 70 run hours at $28 wage | $1,960 |
| Overhead | 100% of labor dollars | $1,960 |
| Total cost | $7,720 | |
| Profit | $10,000 less $7,720 | $2,280 (22.8%) |
Now add what actually happened but never made it to the job sheet:
| Missed cost | How it was figured | Amount |
|---|---|---|
| Setup labor | 8 hours at $28 | $224 |
| Overhead on setup hours | 100% of setup labor | $224 |
| Payroll burden | 30% on 78 total hours at $28 ($2,184) | $655 |
| Scrap allowance | 4% of material | $152 |
| Outside anodizing | Vendor bill coded to general expense | $450 |
| Freight out | Not billed to customer | $180 |
| Programming | 5 hours at $45 | $225 |
| Total missed | $2,110 |
Full cost is $7,720 plus $2,110, or $9,830. The profit on a $10,000 job is $170, about 1.7%. The job didn't change. Only the cost picture did.
The 30% burden here is just for the example. Use your own number. The point is that no single line looks big, and together they took almost all of the margin.
How do you find the gaps in your own job costs?
I think the fastest test is a reconciliation, not a new system. Take last quarter and compare two numbers:
- Total cost charged to all jobs that closed in the quarter.
- Total cost of goods sold on your P&L for the same quarter, adjusted for the change in work in process.
If the jobs add up to a lot less than the P&L, the difference is cost that never reached a job. That gap is your hidden cost. Then you go line by line: which accounts on the P&L have no job-level detail at all?
After that, pick three recent jobs, one good, one average, one bad. Walk each one with the shop lead. Ask what happened that isn't on the job sheet. It's usually setup, rework and outside processing.
How often should you update the rates?
At least once a year, and any time something big changes: a wage increase, a new machine, a new building, or a big shift in volume.
Between updates, watch the gap between overhead you applied to jobs and overhead you actually spent. If it's growing each month, the rate is stale. Don't wait for year-end to fix it.
Once the costs are right, the next step is using them in your quotes. That's covered in how to use job cost reports to sharpen bidding accuracy. If a job has already gone over, see when job costs go over budget.
How we help
We build and maintain job costing for manufacturers as part of our manufacturing accounting and outsourced controller work. That includes the burden and overhead rates, the job sheet, and the monthly check that job costs tie to the P&L.
If your question is mainly about pricing, our pricing and margin analysis starts from full job cost and works out what each job type really earns. We work a lot with CNC and precision machining and metal fabrication shops, where setup and machine time are the usual gaps. Happy to jump on a call if helpful.
Frequently Asked Questions
What costs do manufacturers most often leave out of job costing?
The usual ones are setup labor, payroll burden on labor, machine time, rework, and outside processing. Each one is small on its own, but together they can take most of the margin on a job.
How do I calculate a machine hour rate?
Add up the yearly cost of the machine: depreciation, maintenance, tooling, power and space. Divide by the hours you expect it to run in a normal year, then charge that rate for each hour a job uses the machine.
Should rework be charged to the job or to overhead?
Charge it to the job that caused it. If it goes to overhead, the job looks better than it was and the next quote repeats the same mistake.
How can I tell if my job costs are missing something?
Compare total cost charged to closed jobs with cost of goods sold on your P&L for the same period, adjusted for work in process. A large gap means real costs aren't reaching the jobs.
How often should I update my burden and overhead rates?
At least once a year, and right away after a wage change, a new machine or a big change in volume. If applied overhead keeps drifting away from actual overhead, the rate is out of date.
More on: Cost Accounting
