Construction Contract Types Explained | Projul

Picking the wrong contract type can cost you thousands of dollars on a single job. Pick the right one, and you protect your margins, set clear expectations with your client, and avoid the kind of disputes that drag on for months.

The problem is that most contractors default to whatever contract type they’ve always used. Fixed price for everything, or T&M because “that’s how we do it.” But every project is different, and the contract should match the job, not your habit.

This guide breaks down the five main construction contract types in plain English. You’ll learn when each one makes sense, where the risks are, and how to pick the right structure for your next project.

Fixed Price (Lump Sum) Contracts

A fixed price contract is exactly what it sounds like. You agree to complete the project for one set price. The client knows what they’re paying. You know what you’re earning. Simple.

This is the most common contract type in residential construction and smaller commercial projects. Homeowners love it because there are no surprises on the invoice. And when your estimate is dialed in, it works well for contractors too.

How it works: You estimate the total cost of labor, materials, subcontractors, equipment, permits, overhead, and profit. You present that number to the client. If they agree, that’s the contract price. Period.

Where it works best:

• Projects with a clearly defined scope of work
• Repeat jobs where you know your costs cold
• Clients who need budget certainty (most of them)
• Competitive bid situations

The upside: If you finish under budget, you keep the difference. Your profit margin is built into the price, and efficiency is rewarded. Clients also tend to trust fixed price proposals more because the number is concrete.

The risk: You own every cost overrun. If lumber prices spike, if a sub comes in over budget, if the job takes longer than planned, that all comes out of your pocket. The scope of work becomes your lifeline here. If it’s not in the scope, it’s a change order. That boundary has to be airtight.

Pro tip: Never bid fixed price on a project where you can’t fully define the scope. Remodels with unknown conditions, jobs where the client “hasn’t decided yet” on finishes, or projects with incomplete drawings are all red flags for lump sum contracts. You’ll end up eating costs that should have been change orders, and that’s a fast way to lose money.

Time and Materials (T&M) Contracts

With a T&M contract, the client pays for the actual time your crew spends on the job (at agreed-upon hourly or daily rates) plus the actual cost of materials, usually with a markup.

This is the go-to contract for work where you can’t pin down the scope ahead of time. Service calls, emergency repairs, renovation work where you don’t know what you’ll find once demo starts, and small add-on projects all lend themselves to T&M.

How it works: You set labor rates that cover wages, burden, overhead, and profit. Materials are billed at cost plus an agreed markup (10-20% is common). You track hours and materials daily and invoice on a regular schedule, weekly or biweekly.

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Accurate time tracking is non-negotiable on T&M work. If you can’t show the client exactly how many hours each crew member worked and what materials were used, you’re going to have billing disputes. Document everything.

Where it works best:

• Repair and service work
• Remodels with unknown existing conditions
• Jobs where the owner wants to make decisions as the project progresses
• Small projects where the cost of creating a detailed estimate exceeds the value

The upside: You get paid for every hour worked and every dollar spent on materials. There’s very little financial risk on the contractor side. If the job takes longer because of unforeseen conditions, the client pays for that time.

The risk: Clients can feel uneasy because there’s no ceiling on the cost. Some will question your hours or push back on material receipts. The best way to handle this is to set a not-to-exceed (NTE) cap or provide a rough budget range upfront. That gives the client a ballpark while still protecting you from scope unknowns.

Pro tip: Always define what’s included in your hourly rate. Does it cover truck time? Tool wear? Supervision? Spell it out in the contract so there’s no argument later about what the client is paying for.

Cost Plus Contracts

Cost plus is similar to T&M but structured differently. The client pays for all actual project costs, and then you add a fee on top. That fee is either a fixed amount (“cost plus fixed fee”) or a percentage of total costs (“cost plus percentage”).

This contract type shows up most often on larger projects, custom homes, and jobs where the owner wants full transparency into spending.

How it works: You track and document every project cost: labor (at actual wages plus burden), materials, subcontractor invoices, equipment rentals, permits, and any other direct costs. The client reimburses all of it. Your profit comes from the fee, which is agreed upon before work starts.

Where it works best:

• Custom homes where the scope evolves during construction
• Projects where the owner is heavily involved in decision-making
• Large or complex jobs that are hard to price accurately upfront
• Jobs with a trust-based contractor-client relationship

Cost plus fixed fee vs. cost plus percentage: With a fixed fee, you earn the same profit regardless of what the project costs. That aligns your interests with the owner’s because you’re not incentivized to run up costs. With a percentage fee, your profit grows as the project cost grows, which some owners view with suspicion. Fixed fee is generally easier to sell and builds more trust.

The upside: You’re covered on costs. There’s almost zero risk of losing money because the client pays actual expenses. And the transparency often builds strong relationships with owners who appreciate seeing where every dollar goes.

The risk: Your profit is capped (especially with a fixed fee). If you run the job efficiently, you don’t get to keep the savings the way you would with a fixed price contract. Also, the bookkeeping burden is real. You need solid job costing to track every expense and present clean documentation to the client. Sloppy records will erode trust fast.

Pro tip: If you go cost plus percentage, expect pushback from informed owners. Be ready to justify your percentage and show that your overhead is real. Better yet, offer a fixed fee and stand out from contractors who insist on percentage-based profit.

Guaranteed Maximum Price (GMP) Contracts

A GMP contract is basically a cost plus contract with a ceiling. The client pays actual costs plus your fee, but the total will not exceed a set maximum price. If the project comes in under the GMP, the savings are either returned to the owner or split between you and the owner, depending on the contract terms.

This is popular on commercial projects and with owners who want cost transparency but also need budget certainty. It’s a middle ground between cost plus and fixed price.

How it works: You estimate total project costs and add your fee, contingency, and any allowances. That total becomes the GMP. During construction, you bill actual costs just like a cost plus contract. But if costs exceed the GMP, you absorb the overrun. If they come in below, the savings clause kicks in.

Where it works best:

• Mid-to-large commercial projects
• Owners who want transparency but can’t stomach an open-ended cost plus deal
• Projects where the design is mostly complete but some details are still being finalized
• Construction management at-risk delivery methods

The upside: You get the flexibility of cost plus billing with a cap that makes the owner comfortable. If you negotiate a shared savings clause, you’re rewarded for running the job efficiently. And the GMP can be adjusted through change orders if the owner changes the scope.

The risk: The GMP is your ceiling. If you underestimate the project or miss something in your budget, you pay the difference out of your fee or your pocket. You need a solid estimate and enough contingency built into the GMP to cover surprises. Knowing how to price a job accurately is critical here because your GMP is only as good as the estimate behind it.

Pro tip: Always include a clear contingency line item in your GMP breakdown. Owners will sometimes try to strip contingency out to lower the max price. Push back. That contingency is what protects both of you from unknowns, and it’s standard practice on every GMP contract.

Unit Price Contracts

Unit price contracts break the project down into individual units of work, each with a set price. The total contract price depends on the actual quantities installed or completed.

You’ll see these most often in civil and infrastructure work: road construction, utility installation, excavation, and concrete work. They’re less common in residential, but some contractors use them for repetitive tasks like installing fence posts, pouring footings, or laying tile.

How it works: You bid a price per unit for each work item. For example, $150 per linear foot of trench, $8 per square foot of concrete flatwork, or $2,500 per light pole installed. The owner estimates quantities, but the final payment is based on actual measured quantities.

Where it works best:

• Civil and infrastructure projects
• Jobs where quantities can’t be determined exactly until construction
• Repetitive work with measurable units
• Public works contracts with competitive bidding

The upside: Quantity risk sits with the owner, not you. If they estimated 500 linear feet of trench but the job actually needs 600, you get paid for all 600 at the agreed rate. Your unit price covers your costs and profit per unit, so as long as your pricing is accurate, your margin is protected.

The risk: If actual quantities come in significantly lower than estimated, your total revenue drops, and your fixed overhead costs (mobilization, supervision, equipment) get spread across fewer units. You can protect against this by including a minimum quantity clause or by building mobilization costs into a separate line item rather than spreading them across unit prices.

Pro tip: Watch out for unbalanced bidding in competitive situations. Some contractors front-load early work items and undercut later items to improve cash flow. This is legal in most cases, but savvy owners will check for it during bid evaluation. Price your units honestly and build in a mobilization line item if you need early cash flow help.

How to Choose the Right Contract Type

There’s no single “best” contract type. The right choice depends on the project, the client, and how much risk you’re willing to carry. Here’s a practical framework for deciding.

Start with scope clarity. If the scope is fully defined with detailed drawings, specs, and selections, fixed price or GMP contracts work well. If the scope is fuzzy or likely to change, lean toward T&M or cost plus. A detailed scope of work is the foundation of every good contract, regardless of type.

Consider the client relationship. New clients with no track record may be better served with fixed price, where both sides have clear commitments. Long-term clients who trust you might prefer cost plus, where they see every dollar and you earn a fair fee. The contract type signals something about the relationship, so choose accordingly.

Assess the risk. Who should carry the risk of cost overruns, scope changes, and market fluctuations? Fixed price puts most risk on the contractor. T&M and cost plus shift risk to the owner. GMP splits it. Match the risk allocation to the project’s uncertainty.

Think about your cash flow. T&M and cost plus contracts typically have regular billing cycles (weekly or biweekly), which helps cash flow. Fixed price contracts might have milestone-based payments with longer gaps between invoices. Make sure your invoicing schedule matches your cash needs, especially on longer projects.

Don’t forget about disputes. Every contract type has a different dispute profile. Fixed price fights tend to center on scope and change orders. T&M disputes are usually about hours and markups. Cost plus arguments revolve around what counts as a reimbursable cost. Know where the friction points are and address them in your contract language upfront. A solid understanding of risk management helps you head off these problems before they start.

The bottom line: Match the contract to the job. A kitchen remodel with a finicky client and unknown plumbing behind the walls is a different animal than a ground-up custom home with complete drawings. Use the contract type that protects your profit while giving the client the certainty they need.

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No matter which contract type you choose, the quality of your estimate drives everything. Underbid a fixed price job and you lose money. Overbid a T&M cap and you lose the client. Get your numbers right first, then pick the contract structure that fits. That’s how you build a business that’s profitable on every project, not just the ones that go perfectly.