Cost-Plus vs Fixed-Price Comparison
Model both contract types side by side. See how risk and reward change.
Your best estimate before bidding. The three scenarios assume actual comes in 10% under, on budget, or 15% over.
Fixed-price revenue = expected cost × (1 + markup). Locked in regardless of what actual costs do.
Revenue = actual cost × (1 + rate).
| Scenario | Actual cost | Cost-plus profit | Fixed-price profit | Winner |
|---|---|---|---|---|
| 10% under budget | $450,000 | $54,000 | $125,000 | Fixed-price (+$71,000) |
| On budget | $500,000 | $60,000 | $75,000 | Fixed-price (+$15,000) |
| 15% over budget | $575,000 | $69,000 | $0 | Cost-plus (+$69,000) |
Avg cost-plus profit
$61,000
Avg fixed-price profit
$66,667
Risk-adjusted preference
Fixed-price
Methodology: cost-plus revenue scales with actual cost (or is capped at GMP); fixed-price revenue is locked to expected cost × (1 + markup). Profit = revenue − actual cost in both cases. The three scenarios (10% under, on budget, 15% over) are illustrative; real ranges depend on your estimating accuracy.
Estimates only. Verify with detailed takeoff and current supplier quotes.
Frequently Asked Questions
When is cost-plus appropriate?
Cost-plus shines when scope is genuinely uncertain at the start: early-stage renovations where you can't see behind the walls, design-build with overlapping design and construction, fast-track projects that need crews mobilized before drawings are 100%. It also fits when the owner is sophisticated, wants transparency into actual costs, and is willing to share in the savings as well as the overruns. Avoid it when the owner is new to construction and will struggle to read open-book accounting.
What is a GMP?
Guaranteed Maximum Price is a hybrid: the contractor is paid on a cost-plus basis up to a ceiling, beyond which any overrun comes out of contractor profit. It gives the owner the cost cap of a fixed-price job and the transparency of cost-plus. Most GMP contracts include a savings-share clause (typically 70/30 or 50/50 owner/contractor) so the contractor still has incentive to come in under the cap. AIA A133 and ConsensusDocs 500 are common GMP templates.
How does retainage work on cost-plus?
Retainage on cost-plus jobs usually applies only to the fee, not to reimbursed costs (since costs are documented receipts and the contractor is just passing them through). Common terms are 5-10% retainage on the fee until substantial completion, with the full retainage released at final closeout. On GMP jobs, retainage often applies to the full draw (cost plus fee) up to the GMP cap. Always confirm the retainage scope in the contract because owners and contractors sometimes assume different defaults.
Do owners trust cost-plus accounting?
Sophisticated owners do when the open-book is real: itemized cost ledgers, vendor invoices on demand, monthly reconciliations, and an independent audit clause they can exercise. First-time owners often don't, which is why fixed-price feels safer to them even when cost-plus would price the project more honestly. If you bid cost-plus to a first-time owner, invest time up front explaining what they will see, how change orders work, and what isn't reimbursable. Otherwise expect friction at every draw.