Fixed-Price vs. Cost-Plus vs. Time-and-Materials Contracts

It comes down to who carries the risk

Every pricing model is really answering one question: when the job costs more than expected, who eats the difference? That's the lens to use. Match the model to how predictable the work is, and both you and the client come out fair.

Fixed-price (lump-sum)

You quote one total number for a defined scope, and that's what the client pays, regardless of what your actual costs turn out to be.

Who carries the risk: you do. If materials spike or the job takes longer than you figured, that comes out of your margin. If you're efficient and prices hold, you keep the upside.

When it makes sense: well-defined jobs with a clear, complete scope, like a kitchen remodel with finishes selected or a deck build from a known plan. When you can estimate the work accurately, fixed-price is clean, and clients love the certainty of a single number.

The catch: it's only as safe as your scope and your estimate. Vague scope plus fixed-price is how contractors lose money. This is why the scope and change-order clauses matter so much here: anything outside the defined scope has to become a change order, or you'll absorb it for free.

Cost-plus

The client pays your actual costs (materials, labor, subs) plus an agreed markup, either a percentage or a fixed fee. You share receipts; they see what things really cost.

Who carries the risk: the client does. If costs run high, they pay more; if costs come in low, they pay less. Your markup is protected either way.

When it makes sense: jobs where the scope genuinely can't be pinned down up front, like a gut renovation where you don't know what's behind the walls, or a custom build with evolving selections. Cost-plus lets the work proceed without you gambling on unknowns.

The catch: it demands transparency and trust. The client sees your costs, so your markup is visible, and some clients get uneasy watching an open-ended total climb. Many cost-plus contracts add a guaranteed maximum price (GMP), a cap that says "cost-plus, but never more than X," to give the client a ceiling while keeping the flexibility.

Time-and-materials (T&M)

You bill an hourly (or daily) labor rate plus the cost of materials, as the work happens. Similar to cost-plus, but usually structured around published rates rather than open-book receipts.

Who carries the risk: mostly the client, since they pay for the time and materials actually used.

When it makes sense: small, open-ended, or hard-to-scope work: repairs, diagnostics, "start here and we'll see what we find" jobs, or work where the extent only becomes clear once you're in it.

The catch: clients can feel exposed to an open meter, and disputes over hours are common if you're not documenting well. A clear daily log is your best friend on T&M work; it's the record that justifies every billed hour. Rate caps or not-to-exceed limits can reassure a nervous client.

A quick way to choose

• Scope is clear and complete → fixed-price. Certainty for the client, upside for you if you're efficient.
• Scope is genuinely unknown → cost-plus, ideally with a guaranteed maximum price.
• Small, open-ended, or exploratory → time-and-materials, with good documentation and maybe a cap.

Many residential jobs even blend models: fixed-price for the defined parts, plus an allowance or T&M line for the unknowns. What matters is that the model, and how it handles overruns, is written into the contract so nobody's surprised.

Whichever you choose, the fundamentals hold

No matter the pricing model, the contract still needs a clear scope, a payment schedule, and an ironclad change-order process. See what every residential construction contract needs. And in every case, your quoted price should trace directly back to your estimate, so the number the client signs is the number you actually built.

That traceability is where a lot of contractors slip: the estimate is built one way and the contract is priced another. TradesMetrics carries your estimate straight through to the contract, fixed-price total or cost breakdown, so the pricing model you chose is reflected accurately in the document your client signs, with change orders handled the same way.

Where to go next

Cover the rest with what every residential construction contract needs and deposits, cancellation & the fine print. For the full picture, see the contracts hub and the construction project management pillar.