A guaranteed maximum price is a contractual cap on what a project will cost you. If the work comes in under the cap, you keep the difference or share it depending on the agreement. If it comes in over, that is the builder's problem, not yours.
That is a genuine and valuable protection. It is also routinely oversold, and an owner who signs one believing it makes every surprise impossible is going to have a bad year. Here is the honest version.
What the cap actually covers
A GMP covers the cost of building the scope defined in the contract documents at the time the GMP was set. Inside that boundary, the risk genuinely transfers. Material price increases, subcontractor pricing, productivity, rework, coordination failures, and ordinary field problems are all absorbed by the party who guaranteed the number.
That last point is where most of the value sits. On a traditional project, every ambiguity between the drawings and the field becomes a change order priced when you have no leverage. Under a GMP, ambiguity is the guarantor's problem, which changes their incentive: they now want the documents to be complete and coordinated, because they are the ones eating the gap.
The four things that can still move it
1. You change the scope. This is the big one and it is entirely within your control. If you add a room, upgrade a finish, or change the program after the GMP is set, the price moves. That is not a loophole, it is the contract working correctly. The discipline required is yours: decide before the GMP, not after.
2. Genuinely concealed conditions. On renovation and adaptive reuse especially, nobody can see inside a wall, under a slab, or behind a facade until it is open. A well-written GMP names which conditions were investigated and priced and which are carved out. Read that section carefully. If a GMP claims to cover everything on a hundred-year-old building without any investigation having happened, the number is not real.
3. Owner-caused delay. If approvals sit on your desk for six weeks, or a decision you owe does not arrive, the schedule moves and cost follows. Guarantors are entitled to relief for delays they did not cause. Know what your decision obligations are before you sign.
4. Force majeure and regulatory change. Genuinely extraordinary events and changes in code or law after the GMP date are typically excluded. This is standard and reasonable across the industry.
The question that separates a real GMP from a marketing one
Ask this: at what design stage is the GMP being set, and on what documentation?
A GMP set on a napkin sketch is a guess wearing a contract's clothing. It will be padded heavily to protect the guarantor, or it will be thin and generate a fight later. A GMP set on well-developed documents, with the existing conditions actually investigated, is a number both parties can stand behind.
This is why FrameworkBuild engagements begin with a Design Framework Report. The DFR is what makes the guarantee meaningful, because you cannot honestly cap a price on a project nobody has defined.
GMP is not the same as fixed price
A fixed or lump-sum price is one number, full stop, and any savings belong to the builder. A GMP is a ceiling over an open book: costs are documented, and underruns typically return to the owner or get split by an agreed formula.
For a public owner or a nonprofit board, the open-book part matters as much as the cap. You can show a funder exactly where the money went, which is difficult under a lump sum.
Questions to ask before you sign
- What design stage is this GMP based on, and what documents define the scope?
- What existing-conditions investigation was done, and what is explicitly carved out?
- How much contingency is inside the GMP, who controls it, and what happens to what is left?
- How are underruns shared?
- What are my decision deadlines, and what happens if I miss one?
- Who guarantees it, and what happens if that entity cannot perform?
Why it is worth doing anyway
None of these caveats undermine the core point. A GMP moves the cost risk from the party least able to manage it, you, to the party best able to, the people actually running the work. For an organization accountable to a board, a council, or a community, a defensible number set before construction is often the difference between a project that gets approved and one that dies in committee.
Keep reading on why building projects go over budget and the three delivery methods compared.