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Fixed-Price vs. Cost-Plus Construction Contracts in Ontario
Ontario construction pricing
Fixed price vs. cost-plus
Custom homes + renovations
Fixed-Price vs. Cost-Plus Construction Contracts in Ontario
Fixed-price does not mean the final price can never change. Cost-plus does not mean the builder can charge anything it wants. The result depends on the scope, exclusions, allowances, records, fee formula, change procedure and who carries the risk when actual conditions differ from the assumptions.
Fixed pricePredetermined price for defined work
Cost-plusActual defined cost plus agreed fee
Unit priceMeasured quantity × agreed rate
HybridDifferent models for different risks
The contract title does not control the economics.
A document called “fixed-price” can contain unlimited escalation and allowance exposure. A document called “cost-plus” can include a guaranteed maximum price, exclusions and tightly controlled cost records.
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The four pricing models
Fixed or stipulated price
Formula: predetermined price for defined work.
The contractor generally carries more risk that its estimated labour, material and overhead costs will exceed the price, subject to contract adjustments.
Cost-plus
Formula: defined actual Cost of Work plus percentage or fixed fee.
The owner generally carries more risk of actual quantity and price variation, while receiving cost transparency if records are complete.
Unit price
Formula: measured quantity × agreed unit rate.
Useful where the type of work is known but the exact quantity is uncertain, such as excavation, rock or imported granular material.
Hybrid or GMP
Formula: combines models or adds a guaranteed maximum price.
For example: fixed house shell, unit-priced site work, cost-plus owner changes and a GMP subject to listed exclusions.
Canadian standard-form examples: CCDC 2 is a stipulated-price prime contract; CCDC 3 uses actual cost plus a percentage or fixed fee; CCDC 4 uses predetermined unit prices; and CCDC 5B can begin as actual cost plus fee with options including a guaranteed maximum price or conversion to stipulated price. Standard forms still require project-specific schedules and legal review.
Fixed price versus cost-plus at a glance
| Question | Fixed price | Cost-plus |
|---|---|---|
| Starting price | Predetermined for a defined scope. | Budget or estimate; final price depends on actual defined costs plus fee. |
| Design readiness | Works best with complete drawings, specifications, selections and site information. | Can start earlier when design or scope is evolving, but creates greater budget uncertainty. |
| Cost overrun risk | Contractor carries estimating risk within the defined fixed scope; owner carries defined changes, allowances and excluded risks. | Owner generally pays actual allowable cost, subject to caps, exclusions and audit rights. |
| Cost underrun | Usually benefits the contractor unless the contract provides savings sharing or allowance credits. | Usually benefits the owner because actual allowable cost is lower. |
| Transparency | Owner may not receive underlying trade and supplier cost records. | Should provide open-book records, invoices, time sheets and audit rights. |
| Builder fee | Built into the price and not necessarily disclosed separately. | Percentage, fixed fee or another disclosed formula. |
| Change orders | Critical because scope changes alter the predetermined price. | Still required to control scope, fee treatment, authorization and schedule—even if actual costs are reimbursed. |
| Administration | Usually simpler if scope is complete and changes are limited. | Requires disciplined coding, records, approvals, forecasts and reconciliation. |
| Lender fit | Often easier to compare with an approved project budget, but lender advances still depend on value in place. | Requires lender acceptance of budget uncertainty, invoices, contingency and ongoing cost reporting. |
| Main failure mode | Important work is excluded or the “fixed” price can increase broadly. | Cost of Work and fee are vague, records are weak and nobody controls the forecast. |
Fixed-price contracts: what must be fixed
Advantages
- Clearer starting contract amount
- Less day-to-day cost-record review
- Contractor absorbs defined estimating errors
- Easier owner and lender budget comparison
- Strong incentive to manage labour and procurement efficiently
Risks hidden inside “fixed”
- Incomplete design creates later changes
- Low allowances understate the likely finish cost
- Broad exclusions transfer risk to the owner
- Price-escalation wording weakens price certainty
- Unknown-site clauses can become open-ended extras
A proper fixed-price agreement defines
1
Complete contract documents
Every drawing, specification, quotation and revision used to price the work.
Every drawing, specification, quotation and revision used to price the work.
2
Included work
Measurable labour, materials, systems, finishes, quantities and responsibilities.
Measurable labour, materials, systems, finishes, quantities and responsibilities.
3
Exclusions
Permits, utilities, site work, design, fees and owner-supplied items not in the price.
Permits, utilities, site work, design, fees and owner-supplied items not in the price.
4
Allowances
Quantity, product basis, installed treatment, markup, overage and credit formula.
Quantity, product basis, installed treatment, markup, overage and credit formula.
5
Price-adjustment events
Owner changes, defined escalation, concealed conditions, taxes or government changes.
Owner changes, defined escalation, concealed conditions, taxes or government changes.
6
Change-order procedure
Written scope, price, credit, markup and schedule effect before work whenever practical.
Written scope, price, credit, markup and schedule effect before work whenever practical.
7
Schedule assumptions
Start conditions, owner decisions, long-lead items and allowable delays.
Start conditions, owner decisions, long-lead items and allowable delays.
8
Payment and holdback
Objective milestones, invoices, lender timing and statutory holdback.
Objective milestones, invoices, lender timing and statutory holdback.
Fixed price is not a promise to build an undefined project for one number.
The more incomplete the drawings and selections, the more the agreement depends on assumptions, allowances and change orders.
Cost-plus contracts: define “cost” before defining the fee
A cost-plus agreement should not merely say, “Owner pays all costs plus 15%.” The contract must define allowable and non-allowable costs, supporting records, timing, fee calculation, budget reporting and owner approval.
Percentage fee
The builder earns an agreed percentage of defined actual cost.
Allowable Cost of Work × fee percentage
Fixed fee
The builder receives a predetermined fee in addition to defined actual cost.
Allowable Cost of Work + fixed builder fee
GMP structure
Actual allowable cost plus fee, limited by a guaranteed maximum price subject to stated adjustments and exclusions.
Actual cost + fee, not exceeding adjusted GMP
Illustrative percentage-fee calculation—not a recommended fee
Assume the contract permits a 15% fee on CAD $500,000 of allowable project cost:
| Allowable Cost of Work | CAD $500,000 |
| 15% builder fee | CAD $75,000 |
| Subtotal before HST | CAD $575,000 |
That calculation is only correct if every CAD $500,000 item is included in the fee base. The contract must say whether the fee applies to labour burden, equipment, permits, design, insurance, change work, subcontractor markups, taxes and owner-direct purchases.
Illustrative fixed-fee calculation
Assume actual allowable cost is CAD $500,000 and the agreed fixed builder fee is CAD $70,000:
| Allowable Cost of Work | CAD $500,000 |
| Fixed builder fee | CAD $70,000 |
| Subtotal before HST | CAD $570,000 |
A fixed fee does not make the total project price fixed. Actual allowable cost can still rise or fall unless the agreement includes a ceiling or GMP.
What belongs in the Cost of Work?
| Cost category | Questions the contract must answer |
|---|---|
| Trade contractors | Actual invoices? Tendered amounts? Related companies? Trade markups? Retainage and discounts? |
| Materials | Supplier invoice, freight, storage, waste, restocking, credits, rebates and returns? |
| Builder labour | Named employees, hourly rates, overtime, payroll burden, benefits, vacation and supervision? |
| Project management | Included in the fee or charged as Cost of Work? Which staff, rates and time records? |
| Equipment | Third-party rental, builder-owned equipment, hourly rates, fuel, mobilization and idle time? |
| Temporary facilities | Toilet, fencing, heat, electricity, security, bins, trailers and winter protection? |
| Design and consultants | Architect, engineer, survey, testing and permit-expediting costs included or owner-direct? |
| Insurance and bonds | Project-specific premium, deductible, performance bond, payment bond and course-of-construction coverage? |
| Permits and fees | Municipal, development, conservation, utility and inspection fees included in cost and fee base? |
| Corrections and rework | Does the owner pay for builder error, subcontractor default, uninsured damage or failure to follow documents? |
| General overhead | Office rent, accounting, vehicles, estimating, software and corporate administration included in fee or reimbursed separately? |
| Taxes | Is the fee calculated before or after HST? Are recoverable tax credits excluded from actual cost? |
Do not pay fee on undefined “all project expenses.” Include a detailed schedule of allowable costs, excluded costs and the exact fee base.
Records and audit rights in a cost-plus contract
1
Original invoices
Supplier and trade invoices tied to the correct project and cost code.
Supplier and trade invoices tied to the correct project and cost code.
2
Time records
Employee name, classification, date, hours, task and approved rate.
Employee name, classification, date, hours, task and approved rate.
3
Equipment logs
Machine, operator, hours, agreed rate and mobilization.
Machine, operator, hours, agreed rate and mobilization.
4
Purchase orders
Commitments compared with the current budget before work proceeds.
Commitments compared with the current budget before work proceeds.
5
Credits and rebates
Returns, volume discounts, refunds and incentives credited to the project.
Returns, volume discounts, refunds and incentives credited to the project.
6
Related-party charges
Disclosure and agreed pricing where the builder buys from an affiliated company.
Disclosure and agreed pricing where the builder buys from an affiliated company.
7
Monthly forecast
Cost to date, committed cost, forecast to complete, fee, changes and contingency.
Cost to date, committed cost, forecast to complete, fee, changes and contingency.
8
Owner access
Digital records provided with each invoice and retained for an agreed period.
Digital records provided with each invoice and retained for an agreed period.
9
Audit procedure
Who may audit, notice, location, confidentiality, corrections and audit cost.
Who may audit, notice, location, confidentiality, corrections and audit cost.
10
Budget warning
Written notice before a category or total forecast exceeds the approved budget.
Written notice before a category or total forecast exceeds the approved budget.
“Open book” is not enough.
The agreement must identify which books, records and source documents the owner receives, how quickly, in what format and what happens when a charge is unsupported.
Cost-plus without records is simply an invoice with a percentage added.
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Markup traps that change the real fee
!
Markup on another markupThe builder adds its fee to a subcontractor price that already contains a disclosed project-management or trade markup.
!
Fee on HSTThe percentage is calculated after tax instead of on the agreed pre-tax cost base.
!
Fee on builder errorsThe owner pays actual correction cost plus a fee when the cause was builder or subcontractor fault.
!
Fee on allowances twiceAn allowance already includes overhead and profit, then receives another percentage when reconciled.
!
Fee on owner-direct purchasesThe builder charges a fee on products the owner purchases and pays for directly without defining the related service.
!
Hidden supervision costSite supervision is charged hourly as Cost of Work while the stated builder fee is described as covering management.
!
Uncredited discountsVolume rebates, early-payment discounts or returned materials do not reduce project cost.
!
No fee adjustment after deletionThe owner deletes work but receives only direct-cost credit, leaving fee or overhead attached to removed scope.
Ontario does not impose one universal builder markup. The agreement must state the percentage or fixed fee, the exact cost base and how credits are calculated.
Allowances, changes and unknown site conditions
| Issue | Fixed-price treatment | Cost-plus treatment | Better hybrid option |
|---|---|---|---|
| Kitchen finishes | Fixed specification or allowance with adjustment formula. | Actual approved cost plus defined fee. | Fixed installation with owner-direct material allowance. |
| Excavation quantity | Included quantity plus unit rate for excess. | Actual equipment, labour and trucking plus fee. | Unit-priced excavation using measured quantities. |
| Rock removal | Excluded or unit-priced after verification. | Actual allowable cost plus fee. | Agreed machine, breaker, blasting and haul rates with daily records. |
| Owner changes | Written change order adjusts price and schedule. | Written authorization controls scope; actual cost and fee follow contract. | Prepriced change rates for common items. |
| Tariff or supplier escalation | Contract must define covered events, evidence, mitigation and calculation. | Actual allowable purchase cost may flow through, subject to procurement and budget rules. | Fixed prices after procurement deadlines; transparent adjustment before commitment. |
| Incomplete design | High change-order risk. | Greater flexibility but budget uncertainty. | Pre-construction cost-plus services followed by conversion to fixed price or GMP. |
Ontario payment, holdback and consumer rules
- Proper invoices: Ontario’s Construction Act defines the information a proper invoice must contain. Since January 1, 2026, a deficient invoice is deemed proper unless the owner identifies the deficiency and required correction in writing within seven days.
- Owner payment: Where prompt-payment provisions apply, the owner generally pays a proper invoice within 28 days or gives the prescribed notice of non-payment within 14 days.
- Holdback: Prompt-payment obligations remain subject to the statutory 10% holdback and current annual-release regime.
- Cost-plus evidence: The construction contract should make source records part of the invoice package even where the statutory definition does not independently demand every audit document.
- Consumer estimate rule: If a written estimate is included in a qualifying consumer agreement, Ontario’s current Consumer Protection Act generally prevents charging more than 10% above it unless the consumer agrees to additional or different work or a new price.
Do not automatically apply the consumer estimate rule to every custom-home or commercial cost-plus agreement.
Its application depends on the parties, transaction and contract. Have an Ontario lawyer assess the specific agreement.
Official references: Ontario Construction Act, Ontario renovation guidance, and Consumer Protection Act, 2002.
Which model is better for your project?
Choose fixed price when
The design and selections are substantially complete, site risk is understood, the owner wants price certainty and the contractor can confidently price the defined work.
Main discipline: complete scope before signing.
Choose cost-plus when
The project is unusually complex, design will evolve, existing conditions are difficult to define, transparency matters and the owner can actively monitor the budget.
Main discipline: records and continuous forecasting.
Choose a hybrid when
Some work is predictable and some is not—for example, a fixed house structure with unit-priced site work and cost-plus owner-directed upgrades.
Main discipline: clearly label which model applies to each scope.
My builder’s view: a complete custom home with finished drawings and selections can suit a fixed price. Early-stage design, major renovation and uncertain site work often benefit from a controlled hybrid—but only with proper reporting and written approval boundaries.
Twenty-four clauses to check before signing
1
Pricing model
Fixed, cost-plus, unit price or hybrid stated for each scope.
Fixed, cost-plus, unit price or hybrid stated for each scope.
2
Contract documents
Drawings and specifications identified by revision.
Drawings and specifications identified by revision.
3
Fixed inclusions
Measurable work and products included in the price.
Measurable work and products included in the price.
4
Exclusions
Items outside the contract and owner responsibilities.
Items outside the contract and owner responsibilities.
5
Allowance schedule
Quantity, product level, overage, credit and markup.
Quantity, product level, overage, credit and markup.
6
Cost of Work
Allowable and non-allowable cost categories.
Allowable and non-allowable cost categories.
7
Fee formula
Percentage, fixed fee or other calculation.
Percentage, fixed fee or other calculation.
8
Fee base
Exactly which costs receive the fee.
Exactly which costs receive the fee.
9
Overhead
What the fee includes versus reimbursable project cost.
What the fee includes versus reimbursable project cost.
10
Related companies
Disclosure and pricing of affiliated suppliers.
Disclosure and pricing of affiliated suppliers.
11
Discounts and credits
Returned materials, rebates and savings reduce cost.
Returned materials, rebates and savings reduce cost.
12
Records
Invoices, payroll, time, equipment and purchase orders.
Invoices, payroll, time, equipment and purchase orders.
13
Audit rights
Access, retention period and correction process.
Access, retention period and correction process.
14
Budget
Approved category and total budget.
Approved category and total budget.
15
Forecasting
Monthly cost-to-complete and variance reporting.
Monthly cost-to-complete and variance reporting.
16
Owner approvals
Thresholds before commitments exceed budget.
Thresholds before commitments exceed budget.
17
GMP
Inclusions, exclusions, contingency and adjustment events.
Inclusions, exclusions, contingency and adjustment events.
18
Unit prices
Measurement method and included components.
Measurement method and included components.
19
Changes
Written authorization, price and schedule effects.
Written authorization, price and schedule effects.
20
Price escalation
Covered events, proof, mitigation and calculation.
Covered events, proof, mitigation and calculation.
21
Invoices
Proper-invoice delivery and supporting records.
Proper-invoice delivery and supporting records.
22
Holdback
10% statutory retention and release procedure.
10% statutory retention and release procedure.
23
Termination
Cost reconciliation, fee entitlement and document turnover.
Cost reconciliation, fee entitlement and document turnover.
24
Final accounting
Closeout statement, credits, unresolved commitments and audit.
Closeout statement, credits, unresolved commitments and audit.
Contract Centre and related guides
Fixed-price versus cost-plus FAQ
Can a fixed-price construction contract increase?
Yes. The price may change for defined owner changes, allowance adjustments, concealed conditions, escalation events, taxes or other contract adjustments. The agreement should identify every permitted route.
Does cost-plus mean there is no budget?
No. A proper cost-plus agreement includes an approved budget, category amounts, contingency, regular forecasts and written notice before commitments exceed the budget.
What is a normal cost-plus markup in Ontario?
There is no universal statutory percentage. The fee depends on scope, risk, services, overhead, project size and market. More important than the percentage is the cost base to which it applies.
Is a guaranteed maximum price the same as fixed price?
No. A GMP generally limits actual allowable cost plus fee, subject to defined adjustments, exclusions and contingency treatment. The owner may still need to understand savings and overrun allocation.
Can a builder charge cost-plus without showing invoices?
The contract determines the records required, but an owner should not accept an open-book cost-plus arrangement without source invoices, time records, credits, forecasts and audit rights.
Which model is better for a custom home?
Fixed price can work well after the design, selections and site investigation are sufficiently complete. Cost-plus or hybrid pricing can be better during evolving design or uncertain work if the owner receives strong cost controls and records.
Does Ontario’s 10% estimate rule cap a cost-plus contract?
Not automatically. The rule applies when an estimate is included in a qualifying consumer agreement, subject to the statute and later agreed changes. An Ontario lawyer should assess the specific project and wording.
Should the owner choose the cheapest pricing model?
No. Choose the model that matches the completeness of the design, uncertainty of the work, owner involvement, lender requirements and strength of the contract controls.
The lowest fee can produce the highest final cost when the cost base is undefined
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Reviewed July 29, 2026. General educational information only. Pricing outcomes depend on the actual contract, documents, records and project conditions. This page does not provide legal, tax, lending or accounting advice.
