How to Actually Work Out Overheads in Your Plumbing Business (The Costs That Eat Your Profit)

SNZ Plumbing Estimating · 2025-02-11

Most plumbers can tell you what the materials cost and roughly how long the job will take. Where it falls apart is everything in between. The plumbing overhead costs that do not show up on a fitting invoice and do not sit neatly against a labour hour, but are very real and are quietly eating your profit margin the whole time.

And if you do not charge for those overheads properly, you are paying for them out of your own pocket without realising it.

Let me walk you through what they actually are, in the real world, not the textbook version.

Overhead costs in a plumbing business are everything that keeps the job running but is not on the tools

The mistake is to think of a job as just materials plus the two blokes swinging the tools. A real job has a whole layer of cost sitting underneath that, keeping it moving. That layer is your overhead.

Here is what it actually looks like on a proper job.

The site supervisor. On a job of any size you need someone running the site. He might pick up the tools some of the time, but he cannot be on them one hundred percent, because he is managing the site. That management time is not billable to a fitting or a length of pipe. It is overhead. And so is his van, his fuel, his registration, his maintenance and repairs. The company carries all of it.

The labourer keeping things moving. Sometimes you need a full-time labourer who is not there to do any one billable task, but to keep the site clean and keep things flowing so the productive guys stay productive.

The background support you never see on site. This is the one people forget, and it is important. Behind every job there is someone working in the background. He is ordering the materials. He is shopping around to find the best prices. He is on the ute, going point to point, picking up deliveries and running them to site.

That background role is not a full-time body sitting on the job for the same hours as the others. It is a support function that keeps happening across the whole job. But it has to exist, and it has to be paid for. Either you build it into your overheads, or you lose productive on-tools time every single time something needs chasing. Either way, you pay for it. The smart operator prices it in. The one who forgets watches his crew keep stopping to go sort things out, and wonders why the job ran over.

The office. If you have an office, that is a fixed overhead before anyone even picks up a tool. The rent. The power and the bills. And the people in it. The person doing the purchasing. The person doing the accounts. The person doing the estimating. None of them are on site, but all of them are a cost that every job has to help carry.

The costs that come with bigger jobs. The overhead is not the same on every job, because different work demands different support. A high-end residential job needs a full-time supervisor, you cannot just send in two boys with no oversight and expect it to work. A tier-two job needs a quality control person in the office doing all the QA documentation. A government infrastructure job needs a site engineer and a project manager. Every one of those is an overhead, and it is tied to the type of job you are doing.

The downtime nobody prices for

Here is a second thing that quietly kills jobs, and it sits right alongside overheads.

When people prepare an estimate, the normal practice is to work out how productive the crew will be and how quickly they will get it done. On paper, in ideal conditions.

But real sites are not ideal. There is always time lost. There are stoppages. There are problems on site. There is a meeting going on. There is stop and start. The work is never one smooth line from beginning to end.

So how do you charge overheads? Per job, not per hour

People ask whether you should work overheads out per hour or per job. In my honest opinion, per hour is too hard to work out realistically. It should be per job.

But, and this is the important part, it depends entirely on the size and type of the job.

If the job is small, say half a house, you honestly cannot charge much overhead at all. There is not much money in it to begin with, and if you load it up with overhead you will price yourself out and not win the work. That is just the reality of small jobs.

But the moment the job gets bigger, the opposite is true. If you do not charge the overheads on a big job, you will lose money. A high-end residential job, a tier-two commercial job, a government infrastructure job, these carry real overhead, the supervisor, the QC person, the site engineer, the project manager, the office, the vehicles, the background support. If your price does not carry those costs, they come straight out of your profit.

That is the balancing act. Too much overhead on a small job and you do not win it. Too little on a big job and you lose money on it. Getting that right for the specific job in front of you is a big part of what estimating actually is.

Why this matters more than most plumbers realise

There is no doubt about it. If you have an office, if you have people working with you, if you have vans on the road, those overheads are eating into your profit margin every single day. The question is only whether you have accounted for them in your price or not.

This is the other half of a truth we have written about before. Your wage is not your profit, and neither is the money that has to cover your overheads. A plumber who prices a job with just materials and the two guys on the tools has left out his own wage and all of this. He feels busy and he feels like money is coming in, but the overheads are quietly taking it back, and he never sees where it went.

It is the same discipline as never copying a price off your mate. You cannot charge for costs you never sat down and worked out.

Where we come in

Working out the real overhead for a specific job, and knowing how much a job of that size and type can actually carry, is exactly the kind of judgement that comes from doing it across hundreds of jobs. That is what we do. When we build you an estimate, we work out what overhead that specific job genuinely needs and make sure you are covered on every aspect of it, whether you are working with tier-three builders, tier two, tier one, or government infrastructure projects. Each of those carries a different overhead structure, and the estimate reflects it. The overheads and the productivity allowances are in there as real, considered numbers, not forgotten and not guessed.

You can see how the hydraulic estimating service works, or look through the case studies to see the range of jobs we price. And if you are pricing civil or stormwater work with a lot of underground pipework, the civil and stormwater estimating is where careful overhead and productivity thinking pays for itself.

Because the overheads do not disappear if you ignore them. They just come out of your profit instead of your price.

This article reflects the author's professional experience in hydraulic estimating across Australia. It is general information about how plumbing work is priced and is not financial or accounting advice. For advice specific to your business, speak to your accountant. Last updated 1 July 2026.