Cost-Plus Contracts for Contractors: How to Price and Bill Them

A cost-plus contract bills the customer for the actual cost of the job, plus an agreed fee on top. The fee is either a percentage of cost or a fixed dollar amount. It suits work where the scope cannot be priced honestly up front, such as renovations behind walls, storm repair, or design-build. It only works if every hour and every receipt is documented, because the customer is paying for your records as much as your labor.

Most contractors meet cost-plus when a fixed price would be a guess. The customer accepts the uncertainty; you accept the paperwork. Done well, both sides trust the number. Done badly, it becomes the most argued-over invoice you send.

This guide covers how the fee works, which cost-plus structure to choose, what counts as a cost, and how to bill it cleanly.

How a cost-plus contract works

There are three moving parts. The cost is what you actually spend: crew labor, materials, subcontractors, equipment, permits. The fee is your pay for running the job and covering the overhead that does not appear on any receipt. The billing rhythm is how often you send the cost and fee to the customer, usually weekly or monthly.

Unlike a fixed-price contract, the total is not known when you start. The customer carries the overrun risk. In return, they get transparency: every dollar traces to a document.

Cost-plus is related to time and materials but not identical. T&M bills hours at a set rate and materials at a markup. Cost-plus bills your real cost and adds a separate fee. That distinction matters for how you keep records, covered below.

Cost plus percentage vs cost plus fixed fee

Cost plus a percentage adds a fee such as 15% or 20% to every dollar of cost. It is simple and scales with the work. Its weakness is incentive: the more the job costs, the more you earn, and customers know it. Many will not sign one without a cap.

Cost plus a fixed fee sets a dollar fee regardless of final cost. A $12,000 fee stays $12,000 whether costs land at $80,000 or $95,000. Customers trust it because you gain nothing from running long. It is harder for you to price, since the fee has to cover overhead and profit for a job whose length you do not know.

A third variant adds a guaranteed maximum or not-to-exceed ceiling: cost plus a fee, capped at an agreed total. Costs under the cap are reimbursed; costs over it are yours. It gives the customer a budget and gives you cost-plus billing on a scope that still has soft edges.

Setting the fee so it actually pays

The fee is not pure profit. It has to carry your overhead and your profit together. Work backward from two numbers.

First, your overhead rate: the share of revenue that goes to rent, insurance, software, office staff, and the truck payments no single job absorbs. Second, the profit you need on top. Add them and you have the minimum fee percentage.

Because this is a fee on cost, not on price, remember the difference between markup and margin. A 20% fee on cost is a 16.7% margin on the total billed. If your break-even and profit targets are stated as margins, convert before you write the number into a contract. The same care applies to materials markup when you choose whether materials sit inside the fee base or carry their own markup.

A worked example. You quote a bathroom remodel on cost plus 18%, and your overhead rate is 11%, leaving about 7 points before taxes and owner pay:

Your gross profit is the fee, $2,583, which is 15.3% of the billed total. Overhead of 11% of revenue is about $1,863, leaving roughly $720 of real profit. That is a thin job, and the example shows why the fee percentage has to be set from your overhead rate, not from what feels reasonable.

What counts as a reimbursable cost

Write the list into the contract. Disputes almost always come from one line the customer did not expect.

Usually reimbursable: direct labor at burdened rates, materials at actual cost (delivery included), subcontractors, equipment rental, permits and inspections, dumpsters and disposal, and job-specific insurance or bonds.

Usually inside the fee, not billed separately: office and admin time, your general liability policy, shop rent, tools you own, estimating time before the contract was signed, and the cost of fixing your own mistakes. See callback and warranty costs for why rework should never reach the customer's bill.

Decide two more items up front. Whether your own time as owner is billed as labor, and at what rate. And how you treat trade discounts: if a supplier gives you 10% off, does the customer see actual cost? Most cost-plus contracts say yes, and honoring it is what keeps the arrangement honest.

Documentation is the product

In a fixed-price job the customer sees a result. In cost-plus they see a ledger. Expect them to check it. Each of these needs a document behind it:

• Labor: dated hours by person and task, not a weekly total.
• Materials: supplier invoices or receipts matched to the job, with quantities.
• Subcontractors: invoices and, where relevant, lien waivers.
• Allocated items: anything shared across jobs, like a bulk purchase, with the allocation method stated.

This is where most small contractors lose margin on cost-plus jobs. If labor is reconstructed from memory on Friday, you under-bill hours you cannot prove. If materials arrive from a truck stock with no job attached, you either eat them or bill them without support. Tracking labor cost per job as work happens is the fix, and so is average-cost inventory, which gives every part pulled from stock a defensible cost.

How to bill a cost-plus job

Bill on a fixed rhythm. Weekly for short jobs, every two weeks or monthly for longer ones. Agree on it in the contract, along with payment terms such as due on receipt or Net 15. Cost-plus invoices should be paid fast because you are funding the costs. Do not let a customer sit on a Net 30 while you pay a subcontractor in 10.

Attach the backup. A cost-plus invoice should list cost by category, the fee line separately, and the supporting documents. Separating cost from fee makes the fee visible, which sounds risky and is actually what builds trust.

Track it against a budget. Even without a cap, give the customer an estimated range and update it when the trajectory changes. An invoice that lands 40% above the range, with no warning, is the one that gets disputed. Change orders still apply: when the customer expands the scope, document it, even if the billing method does not change.

Use progress billing when jobs run long. The same discipline behind progress billing applies, with actual cost taking the place of percent complete.

When cost-plus is the wrong choice

If you can define the scope in a written scope of work and you have real cost history from similar jobs, a fixed price lets you keep the upside of working efficiently. Cost-plus caps how much you can earn from being good at your job. Use it where the alternative is either a padded fixed price, which loses you the bid, or an unpadded one that loses you money. For deciding between these paths, how to bid a construction job shows where the estimate becomes unreliable.

How CRMb supports cost-plus billing

Cost-plus depends on records, which is exactly what CRMb captures as work happens. Crew hours punched in Punch flow into job labor cost, so the labor line is real hours rather than a recollection. Materials pulled from inventory carry average cost. Quotes and invoices go out as public share links the customer can open and sign. And reconciling bank transactions to jobs means the supplier charges on your statement land on the right job. Reports then show margin on real punched hours, so you can see whether your fee is covering what you thought it would. Learn more about job costing, or see the reports and accounting pages.

Frequently Asked Questions

What is a cost-plus contract?

A cost-plus contract has the customer pay the actual cost of the work plus an agreed fee. The fee is a percentage of cost or a fixed amount. The contractor documents every cost, and the customer reimburses those costs at the agreed billing intervals.

What is a typical cost-plus percentage?

It depends on your overhead and trade. Fees commonly land between 10% and 25% of cost. The right number is your overhead rate plus your target profit, expressed as a percentage of cost rather than of price.

Is cost-plus better than fixed price?

Neither is better in general. Cost-plus fits jobs with an unknowable scope, since it shifts overrun risk to the customer. Fixed price fits well-defined jobs where your efficiency becomes your profit. See time and materials vs fixed price.

What is the difference between cost-plus and time and materials?

Time and materials bills labor at hourly rates and materials at a markup. Cost-plus bills actual cost, including real burdened labor, and adds a separate fee. Cost-plus needs more documentation and tends to be more transparent.

How do I stop a customer from disputing a cost-plus invoice?

List reimbursable costs in the contract, attach backup to every invoice, separate cost from fee, and give an estimated range up front. Notify the customer before the total exceeds it.

Can I add a cap to a cost-plus contract?

Yes. A guaranteed maximum or not-to-exceed cap gives the customer a budget ceiling. Costs above the cap are yours, so set it only after you have a reasonable estimate.

Should materials be marked up in a cost-plus contract?

Usually not separately. The fee is your markup. Adding both a materials markup and a fee double-charges the customer and invites disputes unless the contract explicitly allows it.

Getting started with CRMb

CRMb ties crew hours, materials, subcontractor costs, and invoices to each job, so a cost-plus bill is a report you can defend, not a reconstruction. Start a 14-day free trial and run your next open-scope job with real numbers behind every line.