Fixed Price vs. Cost-Plus: Which Contract Is Right for Your Project?

Most homeowners assume that getting a lower quote means paying less. That's not always true. What often matters more than the number itself is the contract structure behind it — and most people don't know that two fundamentally different structures exist, let alone which one is right for their project.

This article explains both. By the end, you'll understand how each one works, when each one protects you, and why choosing the wrong structure — even with a contractor you trust — can create problems that a lower quote won't fix.

The Two Structures

Every construction contract is, at its core, one of two things: a fixed price, or a cost-plus arrangement. Everything else is a variation on those two.

Fixed price (also called lump sum or stipulated price) means the contractor agrees to complete a defined scope of work for a set amount. The price is agreed before work starts, and it doesn't change unless the scope changes.

Cost-plus (also called time and materials, or T&M) means you pay the actual cost of labour and materials, plus an agreed markup percentage. The final cost isn't set in advance — it's the sum of what the work actually costs to execute.

Both are legitimate. Both are used by reputable contractors. The question is never "which one is better" — it's "which one is right for this specific project."

How Fixed Price Works

In a fixed-price contract, the contractor has priced the job, built in their costs and profit margin, and committed to a number. If their labour costs more than expected, or a material price goes up — in most cases, that's their problem, not yours.

This sounds like the ideal structure for a homeowner. And for the right project, it is. Budget certainty is genuinely valuable. Knowing the number before you start means you can plan your finances, make decisions, and commit without anxiety about where the final invoice lands.

But fixed price works well only when three conditions are met:

• The scope is clearly and completely defined before pricing
• The site conditions are well understood before pricing
• The unknowns are limited — or the contractor has been able to assess them properly

When those conditions are met, a fixed-price contract is clean and straightforward. The contractor knows what they're building. You know what you're paying. Everyone moves forward with aligned expectations.

The Hidden Risk in Fixed Price

Here's what actually happens when a contractor gives you a fixed price on a project with unclear scope or unknown site conditions: they have two options. They can price it tight — take the risk, win the job, and hope for the best. Or they can pad the number — build in enough contingency to cover whatever they might find, and protect their margin against the unknowns.

If they price it tight and find problems, they lose money. Contractors who lose money on a job have limited options: absorb it (unlikely), come back to you with change orders (common), or cut corners somewhere to make up the difference (more common than anyone admits).

If they pad the number, you pay a premium for risk that may never materialize. You're essentially buying insurance the contractor is pocketing.

Neither outcome is ideal. The root cause isn't the contractor being dishonest — it's the contract structure being applied to a situation it wasn't designed for.

How Cost-Plus Works

In a cost-plus contract, you pay for what the work actually costs: labour hours at an agreed rate, materials at actual invoice cost, and a markup percentage on top of both. The markup covers the contractor's overhead and profit margin.

Nothing is padded. Nothing is estimated to cover unknowns that haven't shown up yet. If the job goes faster than expected, you pay less. If conditions behind the wall are straightforward, you pay for exactly what was needed — not a contingency that assumed the worst.

The markup percentage is agreed in advance and stated in the contract. You know the rate. You see the receipts. You get documentation of what was spent throughout the project. Done properly, cost-plus is one of the most transparent pricing structures in construction.

The Most Common Misconception About Cost-Plus

The concern most homeowners have about cost-plus is that it leaves the budget open-ended. If there's no fixed number, how do you know what you're going to pay?

This is a fair concern — but it's based on a misunderstanding of how cost-plus is properly managed. A well-run cost-plus project includes a budget estimate upfront. You know the expected range before work starts. The contractor tracks costs in real time and reports them regularly. You can see at any point whether the project is on track, running ahead, or running over — and you can make decisions accordingly.

The risk of cost-plus isn't an open-ended budget. The risk is working with a contractor who doesn't manage it properly. That's why the contractor you choose matters enormously on a cost-plus job.

Which Projects Fit Fixed Price

Fixed price is the right structure when the scope is complete and documented, the site has been properly assessed, and the unknowns are minimal. New construction on a prepared lot, a deck replacement on a well-understood structure, a defined interior fit-out in a space with known conditions — these are situations where the contractor can commit to a number with confidence.

Which Projects Fit Cost-Plus

Cost-plus is the right structure when you're renovating an older home where conditions behind the walls are unknown until exposed, when the design is still evolving, when the scope has significant unknowns, or when you want full transparency into costs. For renovations in older North Shore homes — where knob-and-tube wiring, galvanized plumbing, and moisture damage are genuine possibilities — cost-plus is usually the honest choice.

Why the Right Structure Matters More Than the Quote

Here's the scenario that plays out constantly in residential construction: a homeowner gets three quotes. One is fixed price at $X. One is cost-plus with an estimated range. They choose fixed price because the number looks lower. Partway through the project, the fixed-price contractor starts generating change orders — site conditions they "didn't anticipate," scope that was "outside the original agreement." By the end, the fixed-price job costs more than the cost-plus estimate would have — and the relationship is strained.

This isn't a story about dishonest contractors. It's a story about mismatched contract structures. The most important question to ask when evaluating a quote isn't "is this number lower?" — it's "is this contract structure appropriate for this project?"

What to Look For in a Cost-Plus Contract

If your project is a good fit for cost-plus, a well-structured agreement should include: a clearly stated markup percentage, an agreed labour rate, a budget estimate (not a guarantee, but a reasonable range), documentation of actual costs, and a change management process. These elements are non-negotiable. If a contractor won't tell you their markup, that's a problem.

How We Approach This at Ferguson Brothers

We use both structures depending on what the project calls for. We don't default to one or the other — we look at the scope, the site, and the conditions, and we recommend what we think is the honest choice. For a new deck on a well-understood site with complete material selections: fixed price makes sense. For a renovation in an older North Shore home where we don't know what's behind the walls until we open them: cost-plus is usually the right call. We explain both structures before anything is signed.

The Bottom Line

Fixed price gives you budget certainty — when the conditions support it. Cost-plus gives you transparency and flexibility — when the project calls for it. Neither is inherently better. Both are the right answer in the right situation. Ask your contractor which structure they're recommending — and ask them why. The quality of that answer tells you a lot about how they think about their work.