GMP Contracts Explained: Guaranteed Maximum Price in Construction

What Is a GMP Contract?

GMP stands for guaranteed maximum price. In construction, it means the contract sets a maximum owner-paid amount for the defined work, subject to approved changes, exclusions, allowances, and other contract terms.

A GMP agreement often includes:

• Cost of work
• Subcontractor costs
• Materials and equipment
• General conditions
• Contractor fee
• Contractor contingency
• Allowances
• Unit prices, if included
• Approved change orders
• Documentation and audit requirements

The GMP should be tied to a specific scope basis. That may include drawings, specifications, narratives, addenda, alternates, assumptions, exclusions, and schedule notes.

Basic GMP Formula

A simple planning formula is:

GMP = cost of work + contractor fee + contract-defined contingency and allowances

The actual contract may define these pieces differently. Some costs may be reimbursable. Some may be included in the fee. Some may require approval before reimbursement. The written agreement controls.

GMP vs Lump Sum

A lump sum contract usually gives the owner one fixed price for defined work. The owner may not see the contractor's actual cost detail unless the contract requires it.

A GMP contract usually includes more cost visibility. The owner may review eligible project costs, contingency usage, subcontractor buyout, and payment backup. The contractor still needs strong documentation because cost recovery depends on contract rules.

Review these differences:

• Lump sum focuses on a fixed price for defined scope.
• GMP focuses on a maximum price with cost tracking rules.
• Lump sum risk often sits inside the fixed price.
• GMP risk depends heavily on reimbursable-cost, contingency, allowance, and change-order language.

GMP vs Cost Plus

Cost plus contracts reimburse eligible costs and add a fee, but they may not include the same price ceiling unless the agreement creates one.

A GMP can be described as a cost-plus structure with a maximum price for defined work. That ceiling is useful only when the scope, exclusions, and change process are clear.

What Contractors Should Review

Before accepting a GMP, contractors should review the terms that decide whether a cost is recoverable.

Key review points include:

• Which drawings and specifications form the GMP basis
• Which assumptions and exclusions are attached
• Which direct costs count as cost of work
• How general conditions are billed
• Whether contractor fee is fixed or cost-based
• Who controls contingency usage
• Whether unused contingency is returned, retained, or shared
• How allowances are adjusted
• What documentation supports reimbursement
• Which changes adjust the GMP
• Who carries escalation, design-development, and schedule risk

Use a scope of work template, change order form, and bid proposal template to keep assumptions visible before signing.

Contingency in a GMP

Contingency language is one of the most important GMP sections. The contract should explain:

• Who owns the contingency
• What the contingency can be used for
• Who approves contingency draws
• Whether unused contingency is credited, shared, or retained
• Whether contingency covers design development, coordination, estimating variance, or minor scope gaps
• Which conditions are excluded and handled by change order

Avoid vague language such as "contractor contingency covers all unknowns." Unknowns need boundaries, approval rules, and documentation requirements.

Allowances in a GMP

Allowances are useful when a specific item is known but not fully selected or quantified. Examples can include fixtures, finishes, owner-selected equipment, permits, utilities, or other defined items.

Each allowance should state:

• Allowance item
• Included amount
• Included and excluded scope
• Markup or fee treatment
• Approval process
• Adjustment process if actual cost differs

For more detail, use the construction allowances and contingencies guide.

Open-Book Cost Tracking

GMP contracts often use open-book cost tracking. That means the owner can review eligible costs, invoices, subcontractor billings, and supporting records according to the contract.

Contractors should prepare for:

• Clear job-cost codes
• Subcontract and purchase-order backup
• Change-order logs
• Contingency-use logs
• Allowance reconciliation
• Stored-material documentation
• Retainage and payment backup
• Consistent billing review

Open-book tracking is not only an accounting task. It affects field documentation, procurement, subcontract administration, and project controls.

Shared Savings

Some GMP agreements include shared savings if final eligible cost is below the GMP. The contract should define how savings are calculated.

Review:

• Whether unused contingency is part of savings
• Whether allowances are included
• Whether contractor fee changes
• When savings are measured
• Which unresolved costs are held back
• Who approves the final calculation

Do not rely on a general statement that savings will be shared. The calculation method matters.

Change Orders and GMP Adjustments

A GMP should explain when the maximum price can change. Common adjustment triggers may include owner-directed changes, added scope, excluded conditions, design changes, schedule acceleration, or other contract-defined events.

Before bid submission, ask:

• Which changes increase the GMP?
• What notice is required?
• What backup is required?
• How quickly must pricing be submitted?
• Does the contractor need written authorization before work proceeds?

Use the change order generator to draft review notes before the formal contract process controls.

Bottom Line

A GMP contract can give the owner a price ceiling and give the contractor a structured cost-recovery path, but only when the scope and contract rules are clear. Contractors should review the cost of work, fee, contingency, allowances, open-book documentation, shared savings, and change-order process before accepting the maximum price.

The strongest GMP proposals connect the estimate, schedule, assumptions, exclusions, subcontractor coverage, and contract language in one reviewable package.