GMP, Cost-Plus, or Lump Sum: How to Manage Construction Risk
A construction contract decides one thing: who pays when reality diverges from the drawings. Lump sum puts that risk on the contractor — and prices it into the bid. Cost-plus leaves it with you. GMP splits it, with an open book and a cap. For a $1–3M clinic build-out, matching the structure to how complete your drawings are matters more than the number at the bottom of the bid.
Your attorney will review the construction contract, and they should. But legal review answers a narrow question: are the terms of this structure fair? It can't answer the question that comes before it — is this the right structure at all? That decision usually gets made upstream, by default, the day the GC's proposal arrives formatted as a lump sum and the conversation moves straight to the number.
The structure is a commercial decision, not a legal one. I've built over $100M in healthcare infrastructure across more than a million square feet, and the drawings are always a prediction. The building is reality. The delta between prediction and reality gets measured in dollars, and the contract structure — before any clause your attorney redlines — decides whose dollars.
The system underneath it: risk doesn't disappear when you push it across the table. It gets priced. Every dollar of uncertainty you transfer to the contractor comes back to you as premium, contingency, or exclusion. Every dollar you keep is free — right up until the wall gets opened and it isn't. No structure gives you price certainty, cost transparency, and speed at once. There are only tradeoffs, and the structure you sign is the tradeoff you chose, whether you meant to choose it or not.
What's the difference between lump sum, GMP, and cost-plus?
Lump sum (stipulated sum): one number for the defined scope. The contractor owns overruns inside that scope and keeps whatever they save. You get price certainty — for the scope as drawn. Everything not drawn arrives later as a change order, priced without competition.
GMP (guaranteed maximum price): the contractor bills actual cost of work plus an agreed fee, capped at a guaranteed maximum. Books are open — you see every subcontractor invoice. Come in under the cap and the savings split per a negotiated formula. Come in over, and the contractor eats it.
Cost-plus (time and materials): actual cost plus fee, no cap. Total transparency, zero price protection.
The instinct is to rank these — lump sum safest, cost-plus most dangerous. That's not how it works. Each structure is safe in one information environment and expensive in the others. The variable that decides which one you're in isn't the contractor. It's your drawings.
Lump sum works when your construction documents are genuinely complete: 100% CDs, scope airtight, finishes selected, equipment cut sheets in the drawings. In that environment, contractors can price accurately, bid competitively, and the fixed number means something. Healthcare tenant improvement rarely gives you that environment on the timeline you want. You're often in a second-generation space where nobody knows what's behind the drywall, with a design that's still absorbing input from your clinical team, and a lease clock already running. Sign a lump sum there and you haven't bought certainty — you've bought a bid built on assumptions, with a change-order mechanism standing by to correct each one at 15–20% margins instead of the 2–3% the contractor carried to win the job.
Why is a lump sum bid on incomplete drawings a trap?
The lump sum on incomplete drawings
A $1.6M fixed price wins the bid. Demo opens the walls: the panel can't carry the new load, the plumbing isn't where the as-builts promised, the RTUs are older than the broker's flyer implied. Each condition is real, each is technically outside the drawn scope, and each gets priced by the only contractor mobilized on site. The job closes at $2.1M — and the founder tells people construction "ran over," as if it were weather.
The same building under a GMP
The cap is set at $1.75M — higher than the lump sum bid, which stings on signing day. But the book is open, the contingency is visible and jointly governed, and the unforeseen conditions burn contingency instead of generating marked-up change orders. The job closes at $1.68M, savings split 75/25 in the owner's favor. The founder who signed the "more expensive" contract paid $400K less.
The lump sum didn't fail because the contractor was dishonest. It failed because the price was fiction the day it was signed — a precise number attached to an imprecise scope. In systems terms, the change-order process became the pricing mechanism, and it's the worst pricing mechanism available: no competition, maximum leverage on the other side, and your schedule as the hostage.
The GMP isn't free either. You pay a negotiated fee on top of cost, you spend real energy in the open-book review, and the guaranteed maximum quietly wants to become the actual price if you don't govern the contingency. Two terms decide whether a GMP protects you: who controls contingency draws (require written notice and your approval, or at minimum visibility, before contingency is spent), and how savings split (50/50 is common; 75/25 to the owner is achievable and changes the contractor's incentive to manage cost rather than consume the cap).
How do you actually read a construction bid?
Bid day produces three numbers, and the spread between them is usually 15–25%. The instinct is to read that spread as pricing. It's almost never pricing. It's scope — three different guesses about what you meant, wearing dollar signs.
Three places to look before you look at the total:
Allowances. A $40K electrical allowance is not a price for electrical work. It's a placeholder that says "we'll figure this out later, and later you'll pay actuals." A bid carrying six figures of allowances is a cost-plus contract wearing a lump sum costume. Ask what happens when actuals exceed the allowance — the answer is always the same, and it's always your problem.
Exclusions. The low bid is usually low because it excludes the most: permit fees, utility company charges, low-voltage and data cabling, off-hours premiums, temporary power, final cleaning. None of these disappear. They migrate to your budget, unpriced.
Qualifications. "Assumes existing HVAC is adequate for new layout." "Assumes panel capacity sufficient." Each qualification is a risk the contractor is handing back to you, one sentence at a time. In a clinic build — where the mechanical and electrical loads are the building's real product — these sentences are the bid.
Level the three bids line by line until they describe the same project, and the "low" bid frequently isn't. This is tedious work with a clear payoff, and it's a place where an owner's-side project manager earns their fee several times over. I walked through who does this work, and when they need to be in the room, in The Coordination System.
How does the construction contract interact with your lease?
This dependency is easy to miss for a structural reason: the lease and the construction contract get negotiated months apart, by different people, who may never compare notes.
Your TI allowance is reimbursement, not funding — the landlord pays after work is complete, documented, and lien-released, on the schedule the lease dictates. Your construction contract, meanwhile, obligates you to pay the contractor on its own schedule: monthly payment applications, retainage terms, deadlines with interest behind them. If those two documents don't synchronize, the gap between paying your GC and being reimbursed by your landlord is bridged by exactly one party: you, out of working capital you raised to deliver care.
So the contract's payment mechanics need to be drafted against the lease's draw requirements: payment application formats the landlord will accept, conditional lien waivers timed to draw submissions, retainage release that doesn't stall your final TI payment. I covered the landlord's side of this machine in The TI Allowance Fine Print — the construction contract is the other half of that system, and they have to be built as one.
Which contract structure should you choose?
Match the contract to your information state, not to the lowest number. Complete CDs, tight scope, well-documented space: lump sum, competitively bid — you've earned the fixed price by finishing the drawings. Second-generation space, evolving clinical program, compressed timeline: GMP with owner-governed contingency and a meaningful savings split. Schedule-critical early packages — demo, long-lead equipment, rough-in — while design finishes: cost-plus with a defined scope boundary, converting to GMP or lump sum when drawings complete.
There's one more tradeoff worth naming: speed. Finishing drawings to 100% before bidding is the cheapest path per square foot and the slowest path to opening. Every month of design you skip to start construction sooner gets repaid through the change-order window. Sometimes that's the right trade — a clinic that opens three months earlier can be worth real money in revenue and momentum. But make it as a decision, with the cost visible, not as a surprise you discover in month four of a "fixed price" job. And remember that the contract only gets you to substantial completion — the inspection-to-CO gauntlet still stands between a finished building and an open one.
Your contractor isn't the adversary in any of this. The best GCs I've worked with will tell you plainly which structure fits your drawings — but only if the question gets asked before the proposal format hardens into the deal. The contract isn't a formality that follows the relationship. It's the operating system the relationship runs on when something behind the wall surprises everyone. Sign the one that matches what you actually know about your building — and be honest about how much that is.
Key takeaways
- A lump sum bid on 60%-complete drawings isn't a fixed price. It's an opening position, and the change orders are already scheduled — the contractor just hasn't sent them yet.
- A GMP with open-book accounting buys a capped downside and full cost visibility, in exchange for a fee and a contingency whose ownership you have to negotiate.
- Cost-plus belongs in exactly one place in a clinic build: early work packages where waiting for complete drawings costs more than the pricing risk.
- The number on the bid matters less than the allowances, exclusions, and qualifications behind it. The spread between three bids is usually a scope map, not a price map.
- Your construction contract and your lease are one system: if payment applications, lien waivers, and retainage don't line up with your TI draw requirements, you become the bank.
Frequently asked questions
What is a GMP contract in healthcare construction?
A guaranteed maximum price (GMP) contract has the contractor bill actual cost of work plus an agreed fee, capped at a negotiated maximum. Books are open — you see subcontractor invoices — and savings below the cap are split by formula. For clinic build-outs in second-generation space, it caps downside while keeping costs visible. The key negotiated terms are contingency governance and the savings split.
Is lump sum or GMP better for a clinic build-out?
It depends on drawing completeness. Lump sum works with 100% construction documents and airtight scope — the fixed price is real. With evolving designs or unknown existing conditions, common in healthcare tenant improvement, a lump sum becomes a change-order machine, and a GMP with owner-governed contingency usually produces a lower final cost despite a higher starting number.
What are allowances and exclusions in a construction bid?
An allowance is a placeholder dollar amount for work that can't yet be priced — you pay actuals when they exceed it. An exclusion is scope the bid simply omits: often permit fees, utility charges, low-voltage cabling, and off-hours premiums. Both make a bid look lower than the project will cost. Level all bids line by line before comparing totals.
How much contingency should a clinic build-out carry?
Carry two separate contingencies: a construction contingency of 5–10% (toward the high end for second-generation space with unknown wall and ceiling conditions) and an owner's contingency of 5–10% for scope you add. In a GMP, negotiate who controls the construction contingency — if the contractor can draw it without notice, the guaranteed maximum tends to become the actual price.
When does cost-plus make sense for healthcare construction?
Almost only for early work packages: demolition, long-lead equipment procurement, or rough-in released while design finishes. Cost-plus lets you start without complete drawings, but it has no price ceiling — so bound it to a defined scope and convert to GMP or lump sum once construction documents are done. Running an entire clinic build on cost-plus hands your budget to the meter.
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