Cost-Plus vs Fixed-Price Construction Contracts in Florida: Who Carries the Risk, and How You Get a Real Number

CONSTRUCTION CORPS | CONTRACT GUIDE

By Matt Thompson, Owner and General Contractor at Construction Corps. U.S. Army combat veteran. Licensed general contractor since 2007, first in California; Florida licensed since 2022 (CGC, FBPE, EC, CFC, MRSR, MRSA).

Last updated August 2026. This is the final article in our ten-part homeowner and commercial guide series; the full set is linked at the end.

Key takeaways on cost-plus vs fixed-price contracts

-	A fixed-price (lump sum) contract sets the number before construction: the contractor commits to deliver the defined scope for a stated price and carries the risk of estimating it wrong. A cost-plus contract bills you the actual costs as they happen, plus a fee, and you carry the risk of what actual turns out to mean.
-	Neither model is a scam and neither is charity. They are different answers to one question: who absorbs the gap between the estimate and reality. Fixed price includes a risk premium for certainty; cost-plus trades the premium away and hands you the variance.
-	Most residential cost-plus contracts exist for one reason: the price conversation happened before the design was real. When nobody knows exactly what is being built, nobody can commit to what it costs.
-	A fixed price is only as honest as the documents behind it and the allowances inside it. A lump sum built on thin drawings with teaser allowances is cost-plus wearing a disguise, with the variance arriving later as change orders.
-	Cost-plus has legitimate homes: true discovery work where scope cannot be known up front, and commercial structures like guaranteed maximum price (GMP) contracts with open books and savings splits.
-	Our model removes the reason most cost-plus contracts exist: design first (permit-ready plans you can buy as a standalone step), then a firm fixed price built from those exact drawings, with allowances named and change orders reserved for owner changes and genuinely concealed conditions.

In this article

What is a fixed-price construction contract?
What is a cost-plus construction contract?
1. The two models side by side
2. The risk economics nobody explains
3. Where cost-plus genuinely fits, and where it goes wrong
4. How we get you to a real fixed number
5. Contract hygiene, whichever model you sign
6. Frequently asked questions

Every construction contract is a machine for allocating one thing: the difference between what everyone thought the project would cost and what it actually costs. Fixed-price and cost-plus are the two main designs of that machine, and homeowners are routinely sold each one with a slogan (certainty! transparency!) and without the mechanics. This article explains the mechanics: who carries the risk under each model, what each one does to incentives, where each genuinely belongs, and the questions that expose a bad version of either. It closes with how we structure it at Construction Corps, and why our answer starts with the drawings rather than the contract.

What Is a Fixed-Price Construction Contract?

A fixed-price contract (also called lump sum) commits the contractor to deliver a defined scope of work for a stated total price. The scope is defined by the contract documents: the drawings, the specifications, and the allowances. If the work costs the contractor more than estimated, the contractor absorbs it; if it costs less, the contractor keeps the difference. The price changes only through change orders, which are triggered by owner-requested changes or conditions the documents did not and could not cover. The model's promise is certainty. The model's honesty depends entirely on how real the scope definition was on signing day.

What Is a Cost-Plus Construction Contract?

A cost-plus contract bills the owner the actual cost of the work (labor, materials, subcontractors, equipment) plus a fee, either a percentage of cost or a fixed amount. The owner sees the invoices and carries the outcome: if the project runs efficient, the owner keeps the savings; if it runs long or prices move, the owner funds it. A common commercial variant adds a ceiling: the guaranteed maximum price (GMP) contract, where costs are billed openly up to a cap the contractor guarantees, often with a formula splitting savings below the cap. The model's promise is transparency. Its honesty depends on the definitions: what counts as cost, what sits inside the fee, and what incentive anyone has to finish.

1. The Two Models Side by Side

Element	Fixed Price (Lump Sum)	Cost-Plus
When you know the real number	At signing, for the scope as documented	When the job is finished
Who carries cost overruns	The contractor, within the documented scope	The owner, invoice by invoice
Contractor incentive	Finish efficiently; the margin lives in execution	Depends on fee structure; a percentage fee grows when costs grow, which is the model's known conflict
Owner workload	Approve changes; monitor progress against draws	Review cost documentation continuously; audit what counts as cost
Where the fights happen	Change order pricing and what the documents covered	Cost definitions, fee base, productivity, and when it ends
Best fit	Defined scope on real drawings, which is most residential work done right	True discovery work, and commercial GMP structures with open books

2. The Risk Economics Nobody Explains at the Kitchen Table

Here is the honest version of the comparison. A fixed price is not magically cheaper than cost-plus; it contains a risk premium, because the contractor is selling insurance against the estimate being wrong, and insurance is never free. A cost-plus contract is not automatically cheaper either; it simply hands the variance to you, and the fee often looks smaller precisely because it insures nothing. So the real question is not which model has the lower number on page one. It is: whose balance sheet should absorb the surprise, and what does it cost to move the surprise off yours?

"The size of the risk premium tracks the quality of the information. Price a project from finished, engineered drawings and the premium shrinks, because there is less left to be wrong about."

For a homeowner, the answer is usually structural. A contractor prices risk across many projects a year and can absorb a bad one; a family budgets one project and cannot. That asymmetry is why fixed price, honestly built, is the right default for residential work. But it also points at the third option the two-model debate hides: instead of arguing about who carries the uncertainty, shrink the uncertainty itself. That is not a contract trick; it is a sequencing decision, and it is the one most pricing conversations skip.

3. Where Cost-Plus Genuinely Fits, and Where It Goes Wrong

An honest guide names the legitimate territory:

True discovery work. Scopes that cannot be defined until they are opened: interior demolition of storm-damaged structures, where each wall is a finding, stabilization of failing buildings, and some historic work. Committing to a lump sum on an unknowable scope forces a contractor to price the worst case; cost-plus can genuinely serve the owner there, ideally converted to a fixed price the moment the scope becomes knowable.
Commercial GMP structures. Sophisticated owners with auditing capacity use cost-plus with a guaranteed maximum price, open books, and shared savings deliberately, as a collaboration structure. It works because the owner side can actually read the books.

And the failure mode, which is common enough in residential work to deserve its own warning: cost-plus as a substitute for doing the design work. A percentage fee on an undefined scope means the person controlling the costs earns more as the costs grow, the owner discovers the real number one invoice at a time, and nothing in the structure pushes the job to close. If a contractor proposes cost-plus for a definable project (a kitchen, an addition, a whole-home remodel with drawings), the useful question is: what specifically prevents you from pricing this? If the answer is that the design does not exist yet, the fix is the design, not the contract.

The mirror-image failure exists on the fixed-price side, and owners should know it by name: the disguised lump sum. Thin drawings, allowances set at teaser numbers to win the bid, and a price that was never real, with the variance scheduled to arrive later as change orders. A fixed price is only as fixed as the documents and allowances behind it, which is why our contractor vetting checklist tells you to ask how the number was built, not just what it is.

4. How We Get You to a Real Fixed Number

Construction Corps sells fixed-price construction, and the sequence exists to make the fixed price honest:

Ballpark first, from project history. Our published estimator produces a project-history range in about 90 seconds, so you know the neighborhood before spending anything.
Design and engineering to permit-ready, purchasable as its own step. Many clients buy the plans first as a standalone deliverable they own. An accurate price requires real drawings; this is where the uncertainty, and the risk premium it feeds, gets engineered out.
A firm fixed price built from those exact drawings. The company that drew the plans prices them, so nothing in the documents is a stranger to the estimator. Allowances are named, realistic, and explained line by line before signing.
Change orders with a narrow job description. Owner-requested changes and genuinely concealed conditions, priced in writing before the work proceeds. When the same company designed and priced the project, the gap where surprise change orders breed is structurally smaller.
Payments that follow the statute and the work. A draw schedule tied to progress, written releases with every payment, and final payment closing on the contractor's final payment affidavit, exactly as our Florida lien law guide describes. Florida's deposit law (FL Statute 489.126) binds every residential contractor who takes more than 10 percent up front; our structure is built to make those protections automatic rather than aspirational.

This is the through-line of everything we publish: certainty is not a contract clause, it is a sequence. Design first, price from the design, and the argument between cost-plus and fixed-price mostly dissolves, because the uncertainty both models exist to allocate has already been removed.

5. Contract Hygiene, Whichever Model You Sign

The scope is defined by named documents: drawings by date and revision, specifications, and a written allowance schedule. If you cannot point to the sheet, it is not in the price.
Every allowance has a number you have sanity-checked against real selections, and a written mechanism for reconciling over and under.
The draw schedule tracks completed progress, not the calendar, and every payment is exchanged for a written release (FL Statute 713.20 forms).
On cost-plus: cost is defined in writing (what is in, what is out, how sub markups and supervision are billed), the fee base is stated, records access is contractual, and there is an agreed path to convert to a fixed price once scope is known.
On fixed price: the change order procedure requires written pricing and approval before the work proceeds, and concealed-condition language is specific rather than a blank check.
Final payment closes on the contractor's final payment affidavit (FL Statute 713.06), no exceptions, no friendly shortcuts.

Want a fixed price built from real drawings instead of a guess? Start with the plans.

Call (727) 999-1855

6. Frequently Asked Questions

Which is cheaper, cost-plus or fixed price?

Neither, reliably. A fixed price includes a risk premium for certainty; cost-plus removes the premium but hands you the variance, and a percentage fee grows if costs grow. The honest lever on total cost is not the contract model; it is reducing uncertainty before pricing, which means finished drawings. A fixed price built from real documents needs less premium because there is less left to be wrong about.

What is a guaranteed maximum price (GMP) contract?

A cost-plus variant with a ceiling: costs are billed openly, plus a fee, up to a maximum the contractor guarantees, often with an agreed split of savings if the job finishes under the cap. It is common in commercial construction, where owners have the capacity to audit open books. The guarantee is only as strong as the scope definition beneath it; scope changes move the cap.

Are change orders more common with fixed-price contracts?

Change orders are a feature of fixed-price contracts (the mechanism for pricing what changes) but their frequency is a function of document quality, not the model. A lump sum on thin drawings with teaser allowances generates constant change orders because the price was never real. A fixed price built from complete, engineered documents by the company that drew them reserves change orders for owner decisions and genuinely concealed conditions.

What are allowances in a construction contract?

Placeholder budgets inside a fixed price for items not fully selected at signing, commonly finishes, fixtures, and appliances. Honest allowances are set at realistic numbers for the quality level discussed and reconciled in writing as selections finalize. Teaser allowances, set low to make a bid look cheap, are the most common way a fixed price turns out not to be fixed. Ask to see the allowance schedule and check two or three against real products before signing.

Is a cost-plus contract bad for homeowners?

Not inherently; it is bad for homeowners in the wrong application. For genuinely unknowable scope (storm damage discovery, structural stabilization), cost-plus can be the fair structure, ideally converting to fixed price once the scope becomes knowable. For definable projects, cost-plus usually signals that the design work has not been done, and the owner is being asked to fund open-ended uncertainty that better sequencing would have removed.

What fee do contractors charge on cost-plus contracts?

Fee structures vary too widely for a single honest number, and the headline percentage is the least important term. What decides the real economics: the definition of cost (does it include supervision, tools, insurance), whether subcontractor invoices carry markup inside cost before the fee, the fee base, and records access. Two contracts with identical stated fees can produce very different totals. Read the definitions, not the percentage.

When does a design build fixed price become binding?

In our process, when construction documents are complete: the firm fixed price is produced from the finished, permit-ready drawings, by the company that drew them, and attaches to those documents by name. Before that you have a published-range ballpark and progressively tighter pricing as design matures. You are never asked to commit to a construction number before the drawings exist to support one.

Can a cost-plus contract convert to a fixed price mid-project?

Yes, and well-run discovery projects are structured for exactly that: cost-plus through the unknowable phase (demolition, exposure, stabilization), then a fixed price for the defined rebuild scope once conditions are known. If you are entering cost-plus for a discovery phase, put the conversion mechanism in the contract up front.

How does Florida law protect me regardless of contract type?

The protections travel with the payments, not the pricing model: the deposit duties of FL Statute 489.126 (a contractor taking over 10 percent up front on residential work must apply for permits within 30 days and start within 90 days after permits issue), the release system of Chapter 713, and the final payment affidavit of FL Statute 713.06 before the last check. Our lien law guide and contractor vetting checklist cover the full system.

Who offers fixed-price design-build contracts in Tampa Bay?

Construction Corps delivers fixed-price design build across Pinellas, Hillsborough, Pasco, and Sarasota counties: published ballpark ranges at constructioncorps.com/estimator, permit-ready plans available as a standalone purchase, and a firm fixed price built from those exact drawings, as a veteran owned general contractor with six in-house Florida licenses (CGC1530192, FBPE39242, EC13013956, CFC1432954, MRSR5676, MRSA5772). Call (727) 999-1855.

Certainty Is a Sequence, Not a Clause

Construction Corps is a veteran owned design build general contractor based in Clearwater, serving Pinellas, Hillsborough, Pasco, and Sarasota counties. We price the way this article recommends: a published ballpark first, permit-ready plans you can buy as their own step, and a firm fixed price built from those exact drawings, with allowances named, change orders narrow, and payments running the statutory release chain.

This article closes our ten-part guide series for Tampa Bay homeowners and commercial owners: veteran-owned contracting, hurricane rebuilds, addition costs, the FBC 9th Edition, design-build delivery, lien law, permit timelines, contractor vetting, ADU conversions, and contracts. Start anywhere; they all point at the same idea. Know the system, and the system protects you.

About Construction Corps

Construction Corps, Inc. is a veteran owned, full service design build general contractor headquartered at 2054 Weaver Park Drive, Clearwater, Florida 33765. Founded in 2022 and led by Matt Thompson, a U.S. Army combat veteran (Infantry, 11B) with more than 30 years of construction experience, first licensed as a general contractor in California in 2007 and licensed in Florida since 2022, Construction Corps serves residential and commercial clients across the Tampa Bay region, including Pinellas, Hillsborough, Pasco, and Sarasota counties. The firm is an SBA certified Service-Disabled Veteran-Owned Small Business (SDVOSB) and Veteran-Owned Small Business (VOSB). Construction Corps delivers design build as one company, as full projects or plans first, at a firm fixed price built from its own drawings, holding Florida licenses CGC1530192 (general contractor), FBPE39242 (Florida Board of Professional Engineers), EC13013956 (electrical contractor), CFC1432954 (plumbing contractor), MRSR5676 (mold remediation), and MRSA5772 (mold assessor). Published project pricing is available at constructioncorps.com/estimator. Phone (727) 999-1855.

Sources Cited

FL Statute 489.126 (deposit duties: permits within 30 days, work within 90 days after permits, on initial payments over 10 percent): flsenate.gov/laws/statutes/2025/489.126
FL Statutes 713.06 (final payment affidavit) and 713.20 (waiver and release forms): flsenate.gov/laws/statutes
Construction Corps pricing process (ballpark, plans, fixed price) and published ranges: constructioncorps.com/estimator and constructioncorps.com/our-process
Related guides in this series: Design-Build vs Design-Bid-Build; Notice to Owner and Florida Lien Law; How to Vet a General Contractor in Florida

This article is general information about contract structures, not legal advice, and no statement here is a quote or pricing commitment. Contract terms are project specific; review any construction contract with a Florida construction attorney where the stakes warrant it.

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