How cost plus pricing works

With a fixed-price estimate, you promise a number upfront and absorb whatever the job actually costs. Cost plus flips that around. The customer agrees to pay what the job really costs — your labor hours, materials at what you paid, subcontractors at their invoices — plus a percentage or flat fee that is your profit and overhead recovery.

Say your agreed markup is 20% and a bathroom remodel racks up $9,000 in documented costs. The customer pays $10,800. If costs come in at $11,000 instead, they pay $13,200. The percentage stays fixed; the total floats with reality.

That floating total is the defining feature, and it is why the paperwork matters so much. Every cost you bill has to be real, recorded, and showable. Cost plus is not a handshake and a number at the end — it is a running account of the job.

When cost plus is fair to both sides

Cost plus earns its keep when honest scoping is impossible. Opening walls in an old house, repairing hidden water damage, restoring after a storm — nobody can price that work fixed without either padding heavily or gambling. Cost plus lets the job start now and lets the price follow the truth.

It is also fair when the customer values speed or flexibility over price certainty. A homeowner who wants work to start tomorrow, or one who keeps upgrading finishes mid-job, gets exactly what they asked for and pays exactly what it cost.

It is a poor fit for small, well-defined jobs. If you can scope the work in one visit, a fixed price is simpler for everyone, and most customers prefer the certainty. For the fixed-price side of the trade-off, see how to price contractor jobs.

Open book is the whole deal

Cost plus only works if the customer can see the costs. That means supplier receipts, subcontractor invoices, and timesheets available on request — or better, shared with each progress billing without being asked. Contractors who treat the books as private give cost plus its bad reputation.

Go in expecting questions about the numbers. If your records answer them in seconds, the arrangement builds trust instead of eroding it. If they do not, every invoice becomes a negotiation.

Agree upfront on what counts as a cost. Is your truck time a cost? Tool wear? The trip to the supplier? Spell it out in writing before work starts, because mid-job is the worst time to define terms.

Caps and GMP in plain terms

The customer's obvious fear is a blank check. The standard answer is a cap, often called a guaranteed maximum price, or GMP. You agree the total will not exceed a set number. Costs below the cap are billed at actuals plus markup; if costs run past the cap, the overage is your problem, not the customer's.

A GMP splits the risk. The customer gets a ceiling, and you keep the flexibility to deal with surprises without renegotiating every discovery. Some agreements add a shared-savings clause: if the job finishes under the cap, the savings are split between you and the customer, which gives both sides a reason to run lean.

Set the cap honestly. A cap you expect to blow through is a fixed-price contract in disguise, with worse paperwork.

Whatever structure you choose, put the markup percentage, the definition of a billable cost, the cap if any, and the billing rhythm in writing before the first day of work.

Risks on both sides of the table

  • For the customer: without a cap, costs can drift upward with no natural brake, and there is little built-in pressure to finish fast.
  • For the customer: you are trusting the contractor's bookkeeping, so vague records are a red flag.
  • For the contractor: sloppy tracking means unbilled costs you end up eating, and disputed receipts can stall payment for weeks.
  • For the contractor: with a GMP, overruns past the cap come straight out of your pocket.
  • For both: scope creep disguised as cost plus can hide a job that was never really defined at all.

Put the agreement in writing

A cost plus job still starts with an estimate — not a fixed price, but a written description of the expected scope, the cost categories, the markup, and the cap. The customer should be able to read one document and know exactly how the final number will be built. Our pillar guide on how to write an estimate covers the document itself.

EstimateBook drafts itemized estimates from voice, text, or photo on iOS and Android, and you review and edit every line before sharing it as a PDF — a clean starting document for a cost plus agreement. The draft is a starting point; the final numbers and terms are always yours to check. And since cost plus lives or dies on markup, contractor markup explained helps you set the percentage.