Why that "profitable" job might have lost you money
Job costing is checking a finished job against your quote. Take what you charged, subtract what it actually cost in labour, materials and extras, and that is your real profit. Do it regularly and two things almost always show up: labour running over, and materials costing more than planned. Catch those and your next quote is sharper.
A job can feel profitable and still not be. The invoice was a decent size, the customer was happy, nothing obviously went wrong, so you file it as a good one and move on. Then, if you ever actually sit down and add up the real hours and the real materials bill, the profit is often a lot thinner than it felt, or gone completely.
Job costing is the habit that catches this before it becomes a pattern. It takes a few minutes, and it turns a feeling into a number.
The two things that quietly kill profit
Cost enough jobs and you will find the damage almost always comes from the same two places.
Neither one looks dramatic on its own. A couple of extra hours here, a bit more timber there. But stack them up across a run of jobs and they are usually the whole gap between what you thought you earned and what actually landed in the business.
A worked example
Say you quoted a job at $1,650, expecting it to cost you $1,320, for a planned profit of $330. Here is what actually happened once the work was done: 18 hours of labour at $50 an hour, and $450 of materials.
| Price charged | $1,650 |
| Actual labour (18 hrs × $50) | $900 |
| Actual materials | $450 |
| Actual cost | $1,350 |
| Actual profit | $300 |
| Actual margin | 18% |
| Versus quoted profit ($330) | −$30 |
The job still made money, $300 is not nothing, but it fell $30 short of the plan, purely because those extra two hours of labour cost more than the buffer had room for. On its own that is a rounding error. If it happens on every job of that type, it is telling you something about how you quote that type of job.
What to actually do with what you find
- Feed it back into your quotes. If a certain type of job always runs two hours over, price two hours in next time. That is not padding, it is accuracy.
- Look for the pattern, not the one-off. One bad job is bad luck, materials that spiked or a customer who changed their mind halfway through. The same overrun showing up on every similar job is a pricing problem, not luck.
- Find your best work. Costing also shows which jobs make the most, quietly, without you having to guess. That tells you what to chase more of.
None of this needs to be a big exercise. Costing your bigger jobs, or even a handful each month, is usually enough to see where the profit is actually leaking.
Frequently asked questions
What is job costing?
What is the difference between a quote and job costing?
What counts as the cost of a job?
What if a job lost money?
How often should I cost my jobs?
The takeaway
Feeling like a job went well is not the same as knowing it made money. Job costing takes a few minutes and replaces the feeling with an actual number, and once you have that number, your next quote gets a little sharper. Do it on enough jobs and the guesswork disappears from your pricing altogether.