Are You Actually Making Money on Every Job? A Contractor's Guide to Job Costing in Sarnia & Southwestern Ontario

My Better Books
13 hours ago
6 min read

By My Better Books | Xero Silver Partner | Xero L2 Certified Professional | Sarnia, Ontario

You're busy. The phone rings, the jobs get done, the invoices go out. Money comes in. So why does it feel like there's never quite enough left at the end of the month?

For contractors and tradespeople across Sarnia, Lambton County, London, and Windsor, this is one of the most common — and most frustrating — financial problems. And most of the time, it's not about how many jobs you're doing. It's about not knowing which jobs are actually making you money.

That's exactly what job costing solves. As a Xero Silver Partner and L2 Certified bookkeeping firm specializing in small businesses and trades across Southwestern Ontario, it's one of the most important tools we set up for our contractor clients.

In this guide, we'll break down what job costing is, why most contractors skip it, and how Xero makes it simpler than you'd think.

What Is Job Costing? (And Why It Matters for Ontario Contractors)

Job costing is the process of tracking all costs — labour, materials, subcontractors, equipment rentals — against a specific job or project. Instead of looking at your finances as one big lump, you break it down project by project.

For trades and contractors in Ontario, job costing answers questions like:

• Did this roofing job actually hit my target margin — or did I leave money on the table?

• Are my estimates for electrical work consistently accurate, or am I underpricing?

• Which types of jobs — commercial vs. residential — are my most profitable?

• Where is my labour cost actually going, compared to what I budgeted?

Without this data, you're making decisions based on gut feel. With it, you can quote smarter, grow intentionally, and stop taking jobs that eat up your time without building your bottom line.

You can be fully booked every week and still go backwards. Job costing shows you which work is worth taking — and what to charge for it.

Why Most Contractors in Sarnia Aren't Tracking Job Costs

Here's the honest answer: nobody showed them how, and the setup feels overwhelming.

Most trades and contractors got into business because they're good at what they do — plumbing, electrical, HVAC, landscaping, construction. Not because they love spreadsheets. So bookkeeping usually means just keeping CRA happy at tax time.

Here's what gets missed without job costing:

• You don't know your real labour cost per job — just what you hoped it would be

• Material overruns quietly kill your margin job after job

• You quote based on last year's prices without realizing costs have shifted

• You can't identify which clients or project types are most profitable

• When it's time to hire, you have no data to base the decision on

The result? A business that looks successful from the outside but is operating on razor-thin margins — or losing money on certain jobs entirely.

A Real-World Job Costing Example for Ontario Tradespeople

Say you're a plumber in Sarnia-Lambton who quotes a bathroom renovation at $4,800.

After the job, you track your actual costs:

• Your labour (2 days): $1,200

• Helper labour: $600

• Materials: $1,350

• Subcontractor (tile work): $700

• Total job cost: $3,850

That's a $950 gross profit — about 20% margin. Not bad. But what if materials ran higher on the next similar job? Without tracking, you'd never see it eating into your profits until you looked at your bank account wondering where the money went.

Job costing turns that guesswork into data you can actually act on.

How Job Costing Works Inside Xero

At My Better Books, we run all our clients on Xero — and as a Xero Silver Partner and L2 Certified Professional firm, we know the platform inside and out. Xero is one of the best tools available for contractor job costing, and it's built right into the platform you're already using.

Xero Projects: Job Costing Built Right In

Xero's Projects feature lets you create a project for each job and assign all related income and costs directly to it. Every supplier invoice, every labour entry, every expense — tagged to the job. You can check profitability on any project in real time from your phone or laptop, without waiting for a month-end report.

Xero also connects seamlessly with tools like Hubdoc for receipt capture and Dext for expense management — less manual entry, cleaner records, and a complete paper trail for every job.

What Gets Tracked Per Job in Xero:

Labour costs (your time, employees, helpers)
Material purchases and supplier invoices
Subcontractor costs
Equipment rental or usage allocation
Overhead allocation (a portion of your fixed costs)

At My Better Books, we set this up as part of our bookkeeping service for contractor clients across Sarnia, London, Windsor, and Lambton County. Every month, you get Xero reports that show job-by-job profitability — so you can see exactly where your business stands.

5 Signs You Need Job Costing in Your Contracting Business

You're consistently busy but your bank account doesn't reflect it
You quote jobs the same way you did 3 years ago without knowing if it's still working
You're not sure which types of jobs or customers are most profitable
You're thinking about hiring and don't know if you can afford it
Tax time is the only time you really look at your numbers

If any of these sound familiar, job costing isn't just a nice-to-have — it's the thing that changes how you run your business.

Frequently Asked Questions: Job Costing for Contractors in Ontario

What is job costing in construction and trades?

Job costing is the practice of tracking all revenue and costs — labour, materials, subcontractors — against a specific project or contract. It lets you see exactly how profitable each job was, rather than looking at your business finances as a whole.

How does Xero handle job costing for contractors?

Xero's Projects feature lets you assign all income and expenses to individual jobs. You can track labour, materials, subcontractors, and overhead per project and see real-time profitability from any device. At My Better Books, we configure Xero Projects specifically for trades and contractor clients across Ontario.

Do I need to switch software to do job costing?

Not if you're already on Xero. Job costing is built right into Xero Projects. If you're on a different platform, we can migrate your books to Xero cleanly as a Xero Migration Specialist firm — and set up job costing from day one.

How is job costing different from regular bookkeeping?

Regular bookkeeping tracks your income and expenses across the whole business. Job costing goes one level deeper — it assigns those numbers to specific jobs so you can see which work is profitable and which isn't. Both are important; job costing just gives you more actionable data.

Can a bookkeeper help me set up job costing in Xero?

Yes — and they should. At My Better Books, job costing setup in Xero is part of what we do for contractor clients in Sarnia and across Southwestern Ontario. As a Xero Silver Partner and L2 Certified Professional firm, we know exactly how to configure it for trades businesses.

About My Better Books — Our Xero Credentials

My Better Books is a Xero-certified bookkeeping firm serving small businesses and individuals across Sarnia, Lambton County, London, Windsor, and Southwestern Ontario. Every member of our team holds Xero certification — so you get consistent, expert-level service on a platform built for modern business.

✔ Xero Silver Partner

Recognized by Xero as an established, high-performing practice. This designation is earned — not bought — through client volume and certified staff.

✔ Xero L2 Certified Professional

Advanced platform certification held by our team — above the standard Advisor level. This means deeper knowledge, better setup, and smarter use of Xero for your business.

✔ Xero Migration Specialist

Already on another platform? We can move your books to Xero cleanly and correctly. No data loss, no downtime, no mess.