Cost-plus contract

How a cost-plus contract works

Under a cost-plus contract, the client pays what the work actually costs plus a fee for the contractor’s overhead and profit. There’s no fixed price. The contractor bills costs as they’re incurred, usually monthly, with invoices, receipts, timesheets and subcontracts as backup, and adds the fee to each bill or at set points.

Everything depends on the definition of cost. The contract should list what’s reimbursable: field labor and at what rate, materials, subcontracts, equipment rental, permits, and job-site costs such as dumpsters and temporary facilities. It should also say what isn’t, such as home-office overhead, which the fee is meant to cover.

Most cost-plus contracts still start from an estimate, so the client has a budget even without a fixed price. Good practice is to report actual costs against that budget with every bill, so overruns are visible while there’s still time to make choices.

Billing usually follows a rhythm: costs for the period, the fee earned on them, any retainage the contract holds, and the budget to date. Some contracts pay the fee in fixed installments instead of with each bill, which smooths cash flow for both sides. Either way, the client should be able to trace every dollar on a bill to a document.

Types of cost-plus contracts

The main difference between versions is how the fee is set and whether there’s a cap.

Some clients distrust the percentage version because the contractor earns more when the job costs more. Federal contracting rules don’t allow the cost-plus-a-percentage-of-cost system at all. A fixed fee or a cap answers that concern.

Whichever structure you use, the fee usually covers home-office overhead and profit, while job-site supervision and general conditions are billed as cost. Some contracts put supervision inside the fee instead. Either works if it’s written down; the dispute comes when it isn’t.

Why cost-plus matters to each side

For contractors

Cost-plus removes the risk of a fixed price on work that can’t be priced accurately: custom homes, remodels with unknown conditions, jobs where the owner is still deciding. The trade-off is more paperwork, open books, and no extra profit for coming in under budget unless the contract shares savings.

Cash flow is often better than on a fixed-price job, because you bill costs soon after they’re incurred instead of waiting for a milestone. That only holds if bills go out on time with complete backup; one missing receipt can hold up the whole payment.

For homeowners and clients

You pay for what the work actually costs, without a contractor’s padding for risk. You also carry the risk of overruns, and you’ll need to review bills and backup. Cost-plus works best with a contractor you trust, a clear budget, and regular cost reports.

How to set up and run a cost-plus job

1. Write the definition of reimbursable cost, including labor rates, how your own equipment is charged, and who keeps supplier discounts and rebates.
2. Set the fee: a percentage, a fixed amount, or a fixed amount with a cap.
3. Give the client a budget estimate and agree how often you’ll report against it.
4. Set up job costing by cost code from the first day, so every receipt lands on the right job.
5. Bill on the agreed schedule with complete backup.
6. Use change orders for scope changes, since they adjust the budget, the fixed fee or the cap.
7. At closeout, reconcile final costs, the fee and any savings split.

The administration is the job on cost-plus work. A client who sees organized backup every month rarely disputes a bill.

Agree, too, on how long the client has to review and pay each bill, and what happens to disputed items. A practical approach is to pay the undisputed amount on time and settle the rest separately, so one questioned receipt doesn’t stall everything.

Cost-plus example with numbers

Say a remodel is estimated at $150,000 in costs. The contractor and client compare a 15% fee with a fixed fee of $22,500, which is 15% of the estimate. Unexpected conditions push actual costs to $162,000, all within the original scope.

With a percentage fee, the overrun raises the fee too: 15% of $162,000 is $24,300. With a fixed fee, the fee stays at $22,500 and the client pays $184,500. Under the percentage fee, the client pays $1,800 more for the same work, which is why many clients prefer a fixed fee once the scope is reasonably clear.

With a $180,000 guaranteed maximum price, the client pays no more than the cap. Cost plus fee would be $184,500, so the contractor absorbs the $4,500 over the cap, and the effective fee drops to $18,000. If the overrun had come from changes the client asked for, a change order would have raised the cap instead.

Common cost-plus mistakes

• A vague definition of cost, leaving supervision, equipment and small tools open to argument.
• Charging your own equipment without agreed rates.
• Marking up subcontracts and also charging a fee on them, without the contract allowing both.
• Keeping supplier rebates the contract says belong to the client.
• Billing without backup, or with receipts from other jobs mixed in.
• Skipping change orders because “it’s cost-plus anyway.” Changes still adjust the budget, the fee or the cap.
• Not reporting against the budget until the money has run out.

Cost-plus depends on trust, and trust depends on records. Clear definitions and clean monthly backup protect both sides.