What Is a GMP Contract and Why Does It Matter for Commercial Owners?

What GMP Actually Means

A Guaranteed Maximum Price contract establishes a ceiling on what a commercial construction project will cost. The contractor agrees that the final cost to the owner will not exceed the GMP—regardless of what happens with subcontractor pricing, labor, or minor scope adjustments within the defined allowances.

That ceiling is only as reliable as the documentation behind it. A GMP backed by a detailed scope document, a line-item budget, a defined allowance schedule, and a clear exclusion log is an owner-protective instrument. A GMP backed by a single number on a cover letter is a number the contractor intends to change through change orders.

What a GMP Package Should Contain

Before an owner signs a GMP, the contractor should deliver a formal GMP package. Every element in that package defines the boundary between what is covered and what is not.

• —Line-item budget: A cost model that breaks the GMP into trade packages, general conditions, contingency, and fee. Not a single lump sum.
• —Allowance schedule: A list of every scope item priced at an allowance rather than a hard number, with a description of what the allowance covers and how overages are handled.
• —Scope document: A written description of what is and is not included in the GMP. The exclusion log is as important as what is included.
• —Owner contingency: A defined percentage set aside for owner-directed scope changes—separate from the contractor's contingency.
• —Change order protocol: Written procedures for how scope changes are identified, priced, and authorized. No work should proceed without a signed change order.

GMP vs. Lump Sum

In a lump sum contract, the contractor takes full cost risk. If subcontractor bids come in higher than expected, that's the contractor's problem. In a GMP contract, the owner participates in the upside: if the project finishes under the GMP, any savings are typically shared according to a defined formula or returned to the owner.

GMP is the preferred delivery structure when design is not yet complete at the time the contractor is engaged. It allows construction to begin—and cost certainty to be established—before every design decision has been finalized.

The Most Common GMP Mistakes

Owners sign GMP contracts and then watch costs exceed the stated maximum. Here's why it happens:

• —Vague or undefined allowances that are easily exceeded without triggering a formal change order process
• —Exclusion logs written in contractor-favorable language that carve out large categories of work
• —Owner contingency that is inadequately sized for the stage of design when the GMP was locked
• —No formal change order authorization protocol—verbal approvals that the owner doesn't recall

Questions to Ask Before You Sign

Before executing a GMP contract, every owner should be able to answer these questions:

• —What is the total allowance exposure if every allowance is fully spent?
• —What is explicitly excluded from the GMP scope?
• —What contingency does the contractor carry and under what conditions can they access it?
• —How are change orders authorized and how fast are they priced?
• —What happens if the project finishes under GMP?

Iron Sparrow Construction is based in North Carolina and takes on commercial and residential construction projects across the United States. Contact our team to discuss your project.