The owner pays the contractor’s legitimate project costs, then adds compensation for profit. Instead of fixing one final amount before work begins, the parties define reimbursable expenses and the method for calculating the fee.
In cost plus contract construction, this flexibility can accommodate design changes, uncertain site conditions, or evolving material needs. A cost reimbursable contract places more cost risk on the owner, but the contractor must prove each charge is allowable and project-related.
Owners use cost-plus when flexibility matters more than a guaranteed price. It suits urgent starts, incomplete designs, uncertain conditions, and complex work that cannot be estimated.
The trade-off is weaker budget certainty. When comparing cost plus vs fixed price, the owner carries exposure when costs rise. A time and materials contract instead commonly bills labor at agreed rates.
Contractors should retain invoices, receipts, payroll records, time sheets, subcontractor bills, equipment logs, purchase orders, and support for overhead allocations. Records must connect each charge to the project. An audit trail protects both parties, makes charges transparent, and resolves questions before they become disputes.
Owners may inspect those records, test compliance, and reject excluded, duplicated, unsupported, negligent, or unauthorized costs. Sales Tax Rules should also be addressed because tax treatment can affect material purchases and reimbursements.
How does a cost-plus contract work if the project ends up far over the original estimate?
The owner generally pays allowable costs even when they exceed the estimate, unless the agreement includes a guaranteed maximum, spending cap, approval threshold, or exclusion. The contractor must still prove the charges were necessary and permitted. Costs caused by negligence, defective work, unauthorized changes, or poor documentation may be rejected, creating disputes over who ultimately absorbs the overrun and consequences.
What expenses can a contractor legitimately include as billable project costs?
Billable costs usually include labor, materials, subcontractors, equipment, permits, insurance, site security, and other direct expenses identified in the agreement. Approved indirect costs, such as supervision or allocated overhead, may also qualify. The contract should define exclusions, markup rules, and documentation standards. Personal expenses, duplicate charges, negligence-related costs, and unsupported amounts are generally not reimbursable directly by the project owner.
The contractor earns profit through the “plus” portion of the agreement. That payment may be a fixed fee, a percentage of allowable costs, an incentive tied to savings or performance, or an award based on the owner’s evaluation. Profit is separate from reimbursed expenses, although the timing of payment and fee calculation should be clearly stated in the contract documents.
The answer depends on the fee structure. With a fixed fee, the owner generally keeps the savings because the contractor receives the same profit regardless of final cost. Incentive arrangements may share savings with the contractor. Under a percentage-of-cost model, lower spending reduces the contractor’s fee. The agreement should explain whether savings affect bonuses, allowances, contingencies, or final compensation calculations.
Understanding Key Factors in Construction helps owners and contractors choose a contract structure that matches the project’s level of uncertainty, budget priorities, and risk tolerance. A Cost-Plus contract provides flexibility for changing project conditions but requires detailed documentation, clear cost controls, and ongoing oversight to manage expenses. Before signing, both parties should define reimbursable costs, the contractor’s fee structure, and reporting requirements to reduce disputes and keep the project on track.
For more than four decades, Bennett Thrasher has provided businesses and individuals with strategic business guidance and solutions through professional tax, audit, advisory, and business process outsourcing services. Contact Mike Reynolds, partner in charge of Bennett Thrasher’s Financial Reporting & Assurance practice, who has industry experience in Construction, or call us at 770.396.2200.
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