There is a question that makes many NZ trades business owners uncomfortable: how much did that job actually cost?

Not the quote. Not the invoice. The actual cost — materials, labour, subcontractors, vehicle time, rework, the hour you spent on the phone sorting out a supplier issue, the two hours of admin to close it out.

Most trades businesses in New Zealand quote jobs and invoice jobs. Very few go back and calculate what each job cost once it is done. This gap — between estimated cost and actual cost — is where profit quietly disappears.

What Is Job Costing?

Job costing is the process of tracking all costs associated with a specific job or project, then comparing those costs to the revenue the job generated. It gives you the actual margin on each piece of work, rather than an assumed or estimated margin.

For a trades business — plumbing, electrical, construction, HVAC, painting, landscaping — job costing is one of the most powerful management tools available. It tells you which types of work are genuinely profitable, which are not, and why.

What to Include in a Job Cost

A complete job cost includes:

Direct materials. Every item of material used on the job, at the actual cost you paid (not the list price, not an estimate). This includes materials that were wasted, returned, or left over.

Direct labour. The actual hours worked by every person on the job, multiplied by their true cost rate. True cost rate is not just the hourly wage — it includes employer contributions, leave entitlements, and any other on-costs. A tradesperson on $35/hour might have a true cost rate of $45–50/hour once all on-costs are included.

Subcontractor costs. Any work subcontracted out, at the actual invoiced amount.

Plant and equipment. If you own vehicles, tools, or equipment used on the job, there is a cost to using them — depreciation, fuel, maintenance. Many trades businesses ignore this entirely, which means the overhead is being absorbed elsewhere rather than allocated to the work that caused it.

Rework and defects. Time and materials spent fixing mistakes or call-backs. This is often the most uncomfortable number to track, but it is real cost.

Job-specific overhead. Any costs directly attributable to the job — permits, inspections, travel to remote sites, specialist equipment hire.

The Labour Rate Problem

The most common job costing error in NZ trades businesses is underestimating the true cost of labour.

Consider a qualified electrician employed at $38/hour. The business owner might quote jobs using $38/hour as the labour cost. But the true cost includes:

• Employer KiwiSaver contributions (3%): $1.14/hour
• Holiday pay (8%): $3.04/hour
• Sick leave provision: ~$0.80/hour
• ACC employer levy: ~$0.50/hour
• Tools, PPE, uniform allowance: ~$1.00/hour

The true cost rate is closer to $44–45/hour. On a 40-hour job, that is a $240–280 underestimate of labour cost. Multiply that across dozens of jobs per year and you have a significant margin leak.

Comparing Estimated vs Actual Costs

The real value of job costing is not just knowing what a job cost — it is comparing what you estimated it would cost to what it actually cost.

When you run this comparison consistently, patterns emerge:

• Certain job types consistently run over on labour (your estimates are too optimistic)
• Certain materials are consistently more expensive than quoted (your supplier pricing is outdated)
• Certain customers generate disproportionate rework or admin time (they are less profitable than they appear)
• Certain team members complete jobs faster and with less rework (they are more valuable than their wage suggests)

These patterns are invisible without job costing. With it, they become actionable.

A Simple Job Costing Process

You do not need expensive software to start job costing. A spreadsheet works. The discipline matters more than the tool.

For each job, record:

1. Job number and description
2. Quoted price (ex GST)
3. Actual materials cost (from supplier invoices)
4. Actual labour hours × true cost rate
5. Subcontractor costs
6. Any other direct costs
7. Total actual cost
8. Actual gross margin ($) and gross margin (%)

Review this at the end of every job. Review the aggregate monthly. Look for patterns quarterly.

Once you have three to six months of data, you will know which types of work to pursue, which to price more carefully, and which to walk away from.

What Job Costing Reveals About Your Business

Beyond individual job profitability, consistent job costing reveals structural issues:

Quoting accuracy. If your actual costs consistently exceed your estimates by 15%, your quoting methodology needs to change — not your execution.

Overhead absorption. If your job margins look healthy but your net profit is thin, your overhead is too high relative to the work you are doing. Job costing makes this visible.

Capacity utilisation. When you know the true cost of each job type, you can make better decisions about what work to take on when you are at capacity — and what to decline.

Team performance. Labour efficiency varies significantly between team members. Job costing makes this visible in a way that annual wages never do.

Job Costing and Business Value

When a buyer assesses a trades business, one of the first questions is: does the owner know their numbers? A business with consistent job costing records — showing stable or improving margins across job types — is significantly more attractive than one where the owner can only point to annual revenue and a rough sense that "it's been a good year."

Buyers and their accountants will attempt to reconstruct job-level profitability during due diligence. If you have already done this work, you control the narrative. If you have not, they will draw their own conclusions — and those conclusions will be conservative.

A well-documented job costing history is one of the clearest signals that a trades business is professionally run. It reduces buyer risk, which increases what they will pay.

Getting Started

If you have never done job costing before, start with your next five jobs. Track every cost. Compare to your quote. Do not worry about historical data — start building it now.

If you have been in business for several years and have never done this analysis, a structured Business Profitability Review can reconstruct the picture from your existing financial records and identify where the margin leakage has been occurring.

For more on improving overall profitability, see our profit improvement service. If overhead and supplier costs are part of the picture, our cost reduction service covers that ground too.

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Ridgeline Advisory is a Christchurch-based business advisory firm helping NZ business owners improve profit, reduce costs and plan succession and exit.

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