Preconstruction — Estimating & Cost

Cost-Plus Contract

The owner reimburses actual costs and pays the contractor a defined fee on top.

Quick Answer

A cost-plus contract reimburses the contractor for the actual, documented cost of the work and adds a fee for overhead and profit. The fee can be a fixed amount, a percentage, or incentive-based. It suits fast-moving or hard-to-define projects because work can start before scope is final, but it gives the owner less cost certainty unless a maximum price is set.

The Full Picture

Cost-plus exists for projects that can't wait for a complete design or a firm scope — emergency repairs, complex renovations, or fast-tracked jobs where waiting to fully price the work would cost more than the pricing uncertainty. It lets construction proceed while the owner pays for what the work genuinely costs, on an open-book basis.

The 'plus' is the contractor's fee, and its form drives behavior. Cost-plus-fixed-fee pays a set dollar amount regardless of final cost, which removes the incentive to inflate costs. Cost-plus-percentage pays a percentage of cost, which is simple but rewards higher spending — so owners often avoid it or pair it with controls. Incentive fees share savings against a target to align both sides.

The open book is central: the contractor exposes actual invoices, labor, and receipts, and the owner (or a third party) audits them. That transparency is the tradeoff for the owner accepting cost risk. Defining which costs are reimbursable — and which are covered by the fee — is the negotiation that makes or breaks a cost-plus arrangement.

Because pure cost-plus offers the owner little cost certainty, it's very often capped with a Guaranteed Maximum Price. That hybrid — cost-plus up to a ceiling, with shared savings below it — is effectively how most CM-at-Risk projects run. Understanding cost-plus is really understanding the engine underneath a GMP.

Real Examples

→Emergency work: After a flood, a contractor starts stabilization immediately on a cost-plus-fixed-fee basis because there's no time to design and competitively bid the repair.
→Open-book audit: The owner's rep reviews the contractor's monthly cost backup — subcontractor invoices, labor timesheets, material receipts — before approving the pay application.
→Cost-plus with a GMP: A complex hospital renovation runs cost-plus but is capped by a GMP, so the owner sees actual costs yet is protected from unlimited exposure.

Common Misconceptions

People assume: Cost-plus means the owner has no cost control.

Actually: Pure cost-plus does expose the owner, which is exactly why it's usually paired with a GMP cap, a fixed (not percentage) fee, and open-book auditing. Well-structured cost-plus gives the owner both transparency and a ceiling.

People assume: Cost-plus-percentage and cost-plus-fixed-fee are interchangeable.

Actually: They create opposite incentives. A percentage fee grows as costs grow, rewarding higher spending; a fixed fee stays constant, so the contractor gains nothing from cost growth. The fee structure, not just the label, determines whose interests are aligned.

Does MeltPlan Solve This?

Not directly

Cost-plus is a contract and cost-administration structure — reimbursing documented costs against a negotiated fee and audit process. That's an accounting and contract-management workflow, not a document-review or takeoff problem, so it falls outside MeltPlan's preconstruction scope. If a cost-plus job carries a GMP, MeltPlan can still help level the bids and takeoffs behind that cap.

Frequently Asked Questions

What are the types of cost-plus contracts?

Cost-plus-fixed-fee (a set fee regardless of cost), cost-plus-percentage-of-cost (fee scales with spending), and cost-plus with incentive or award fees (a target with shared savings). Fixed-fee and incentive structures better align the contractor with cost control.

Why use a cost-plus contract instead of a lump sum?

When the scope can't be defined well enough to price a lump sum — emergency, fast-track, or highly uncertain work — cost-plus lets construction start immediately and pays for actual costs, rather than forcing a risky fixed price on incomplete information.

Is cost-plus open book?

Yes. The contractor exposes actual costs — invoices, labor, receipts — for the owner or a third party to audit. That transparency is the tradeoff for the owner carrying cost risk.

How does a GMP relate to cost-plus?

A GMP is typically cost-plus with a ceiling: the owner reimburses actual costs plus a fee, but never pays more than the guaranteed maximum for the defined scope, with savings below the cap usually shared. Most CM-at-Risk work runs this way.

Related Terms

GMP (Guaranteed Maximum Price)A contract ceiling on what the owner will pay — the contractor absorbs overruns above it.Lump Sum ContractOne fixed price for a defined scope — the contractor owns the cost risk.Unit Price ContractPricing work by the measured unit when the total quantity isn't known yet.PreconstructionEverything a contractor does to plan, price, and de-risk a project before ground breaks.Cost Estimating (Construction)Predicting what a project will cost to build, at a precision that matches the design.GMP ContractA contract that reimburses cost plus a fee but caps the total at a guaranteed maximum.

More Preconstruction — Estimating & Cost Terms

Sources

  1. AIA Contract Documents — A102 (Owner–Contractor, Cost of the Work Plus a Fee with a GMP)
  2. ConsensusDocs — Cost-plus and CM contract forms
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