Cost-Plus vs. Fixed-Price Construction Contracts: Which One Should You Choose?
If you're about to sign a construction contract, the single biggest financial decision you'll make isn't the price — it's the structure. Cost-plus and fixed-price contracts allocate risk in completely different ways, and choosing the wrong one for your project can cost more than every line item combined.
Fixed-price contracts: how they really work
In a fixed-price (or 'lump sum') contract, the builder commits to a single number to deliver the project. Sounds safe — and for the homeowner it can be — but here's what's actually happening behind the scenes.
- The builder prices in a risk contingency, often 5–15% or more depending on how certain the scope is.
- If actual costs come in below the price, the builder keeps the difference.
- Change orders can become a profit center. Every variation is repriced — usually with a markup.
- Substitutions can happen when material costs spike, so the contract should spell out substitution rules.
Cost-plus contracts: how they really work
In a cost-plus contract, you pay the actual cost of materials, labor and subs, plus a transparent management fee (usually a percentage or flat fee). Every invoice is open-book.
- No hidden contingency — savings flow to you.
- Change orders are simple: actual cost plus the same fee.
- Aligned incentives: the builder isn't penalized for using better materials or smarter methods.
- Requires trust and transparency — pick a builder who actually shares the books.
Side by side
| Factor | Fixed-Price | Cost-Plus |
|---|---|---|
| Price certainty | High (on paper) | Lower upfront, accurate at end |
| Risk owner | Builder | Owner |
| Change order friction | High | Low |
| Transparency | Limited | Full open-book |
| Best for | Cookie-cutter, well-defined scope | Custom, evolving, or investment work |
| Hidden cost | Builder contingency (often 5–15%+) | Owner needs to manage scope creep |
Which one should you actually pick?
Pick fixed-price if:
- Your scope is 100% defined and unlikely to change.
- You want maximum predictability and are willing to pay the contingency premium.
- You're a first-time builder and prefer to outsource the cost-management headache.
Pick cost-plus if:
- You're building a custom home or doing investment work where every dollar matters.
- The scope is likely to evolve as the project progresses.
- You value transparency and are willing to engage with the build.
- You have a builder you trust who runs an open book.
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Frequently asked
Is cost-plus always cheaper than fixed-price?
Not always. Owners can save money on cost-plus because they don't pay a fixed-price contingency, but the final cost isn't capped unless you use a guaranteed maximum price (GMP).
What's a typical cost-plus fee?
Cost-plus fees commonly range from about 10–20% of construction cost. Lower fees usually mean less project management — make sure you understand what's included.
Can a contract be hybrid?
Yes. 'Guaranteed maximum price' (GMP) contracts cap the owner's exposure while keeping cost-plus transparency. Useful for investors who need lender certainty.
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