Fixed Price vs. Cost-Plus vs. Time-and-Materials: Which Contract Fits Your Project

The contract type decides who pays when the cost goes up. Choosing the wrong one is how owners end up with surprise invoices, or contractors end up losing money on a "fixed" job whose scope was never fixed.

Fixed price (lump sum)

One price for a defined scope. The contractor carries the risk of cost overruns on that scope.

• Best when: drawings and specifications are complete and the scope is stable.
• Owner advantage: cost certainty; simple comparison of bids.
• Risks: vague scope leads to change-order fights; low bids can lead to corner-cutting; every change gets priced at the contractor's rates.
• Check in the estimate: scope clarity, allowances (are they realistic?), exclusions, how changes are priced.

Cost-plus

The owner pays actual documented costs plus a fee (a percentage or fixed fee).

• Best when: scope is unclear or evolving, the schedule is urgent or the work is complex or renovation with hidden conditions.
• Owner advantage: flexibility; transparent costs.
• Risks: the owner carries cost risk; a percentage fee gives the contractor no incentive to save.
• Check: definition of reimbursable costs, audit rights, markups on subcontractors, fixed fee instead of percentage where possible.

Cost-plus with a guaranteed maximum price (GMP)

Actual costs plus fee, but not above an agreed ceiling. Savings are often shared.

• Best when: design is partly complete and the owner wants flexibility with a cap.
• Check: what is inside the GMP, contingency ownership, how savings are shared, what changes raise the cap.

Time and materials (T&M)

Hourly or daily rates for labor and equipment, plus materials at cost with markup.

• Best when: small or exploratory jobs, repairs, work with unknown scope.
• Risks: open-ended cost. Always require a not-to-exceed amount and timesheets.
• Check: rate sheet, markup on materials, overtime rules, approval for exceeding the cap.

Quick comparison

• Who bears cost overrun? Fixed: contractor. Cost-plus: owner. GMP: contractor above the cap. T&M: owner, unless capped.
• Needs complete design? Fixed: yes. Others: less so.
• Change handling: Fixed: change orders. Cost-plus: absorbed in costs. T&M: continues at rates.

Five questions before choosing

1. How complete are the drawings and specifications?
2. How likely are hidden conditions or design changes?
3. How much budget certainty do you or your lender require?
4. Do you have the time and staff to review cost documentation?
5. Does the contractor have a track record on this type of contract?

Where budgets drift under any type

• allowances set too low (every upgrade becomes an extra);
• unclear exclusions;
• change orders priced without a rule;
• contingency with no owner or no release rule.

Whichever contract you choose, review the estimate and contract together. MEXUM checks for vague scope, unrealistic allowances, inconsistent markups and missing change-order terms before you sign.

Frequently asked questions

What is the difference between fixed-price and cost-plus contracts?

In fixed-price the contractor sets one price for a defined scope and carries cost overrun risk. In cost-plus the owner pays actual costs plus a fee and carries that risk.

What is a guaranteed maximum price contract?

A cost-plus contract with a ceiling: the owner pays actual costs plus fee up to an agreed maximum. Savings may be shared according to the contract.

When is time-and-materials appropriate?

For small, exploratory or repair work with unknown scope. Require a not-to-exceed cap, a rate sheet and timesheets to keep costs controlled.

Which contract type is best for a home renovation?

If the scope is well defined, fixed price gives cost certainty. If hidden conditions are likely, such as an older building, cost-plus with a cap or a fixed price with realistic allowances and a clear change-order process usually works better.