Fixed-Price vs Cost-Reimbursable vs Time-and-Materials Contracts
Contract type is usually chosen by organisational habit. Some places buy everything fixed price because it feels safe, others reimburse cost because that is how they have always engaged consultants, and the choice is rarely connected to the specific uncertainty in the work being bought. It is the most consequential decision in a procurement, because it decides in advance who pays when the thing everybody half-expected actually happens.
Appendix X4 of the PMBOK® Guide Eighth Edition covers the procurement material these sit in, and the way through it is to treat each type as an answer to one question: where does the cost uncertainty live?
Who carries which uncertainty
Fixed price puts it on the supplier. They quote a number, they deliver for that number, and if it costs them more, that is theirs. This works when the scope is genuinely well defined, because the supplier can price it, and it fails badly when it is not: the supplier prices what they can see, and everything beyond that arrives as a variation, negotiated with no competitive pressure whatever. A fixed price on an incomplete design is not a fixed price; it is an opening position.
Cost reimbursable puts it on the buyer. The supplier is paid their costs plus an agreed fee, which suits work that genuinely cannot be defined in advance: emergency remediation, research, first-of-a-kind integration. The buyer gains flexibility and takes on two obligations in return, to verify costs and to manage efficiency, because the contract itself supplies little incentive for either. Where the fee is a percentage of cost, the incentive runs the wrong way entirely, which is why fixed fees and target-cost structures exist.
Time and materials sits between them and leans towards the buyer. Rates are agreed and the quantity is not, which makes it quick to set up and appropriate for short, exploratory or supplementary work. Its characteristic failure is duration: an arrangement entered into for six weeks of specialist help that is still running two years later, with nobody having decided to make it permanent. A ceiling and a review date turn it back into a contract.
What each one costs to administer
Verification effort. Cost-reimbursable work needs somebody checking timesheets, invoices, rates and allocations, and organisations that choose this type without resourcing that check are paying for an assurance they are not performing. Fixed price needs almost none of that, which is part of its genuine appeal.
Change handling. The burden is inverted. A fixed-price contract makes every change a commercial event requiring quotation, negotiation and approval, and on volatile work that machinery can consume more management time than the delivery does. Cost-reimbursable work absorbs change quietly, which is an advantage right up to the point where nobody can say what the final figure will be.
A refurbishment let before the design was finished
A property team was refitting three floors of an office building and let the works fixed price, on a design that was about seventy per cent complete, because the board wanted certainty on the number before committing.
The first floor went well, and the contractor's price held. The second floor produced eleven variations, most of them legitimate: the partition layout changed after the client's own space planning was revised, and the design had never specified the acoustic rating for the glazed sections. Each variation was priced by the only contractor who could do the work, with a programme already committed, which is not a negotiation in any meaningful sense.
The handover inspection on the second floor found the partition run stopping part way down the floor, with the remaining glazed panels stacked in their wrapping against the wall. They had arrived; the instruction to install them was inside a variation still being priced. Everybody was behaving correctly under the contract, and the floor could not be occupied.
The third floor was let differently. The design was completed first, which cost five weeks, and the works were let on a target cost with a shared pain and gain arrangement. The contractor had an interest in efficiency, the client had visibility of cost as it accrued, and the two variations that arose were handled inside the target rather than as commercial events. The final account came in slightly under target, and the property director's summary was that the five weeks spent finishing the design had been the cheapest five weeks in the programme.
Choosing between them
How well is the work defined, honestly? Not how well it could be defined by the time of contract, but how well it is defined now. This question alone eliminates most wrong choices, and the answer is often uncomfortable enough that people prefer not to ask it.
Who can control the uncertainty? Risk should sit with the party able to manage it. Ground conditions, weather and a client's own decision-making are not things a supplier can control, and a fixed price that pretends otherwise is simply a price with a risk premium in it. Productivity, method and sequencing are the supplier's, and they belong on the supplier's side of the line.
Can you administer what you are choosing? A cost-reimbursable contract without the capacity to verify costs, or a fixed-price contract without the capacity to run a change process properly, will underperform whatever the theory says. The right type badly administered loses to a workable type administered well.
For a PMP® candidate, what matters is that contract type allocates risk in advance, so a scenario where a supplier is submitting frequent variations is describing a mismatch between the definition of the work and the contract chosen for it. A response that tightens the change process is managing a symptom of the selection. Situations where each type is defensible and one fits the uncertainty are the sort a structured PMP exam preparation course sets up deliberately.
Take the contract you are currently working under and name the three things most likely to change. Then ask, for each, who pays under the agreement as written. If the answer to all three is the party who cannot control them, the contract will be expensive regardless of how well the work goes, and knowing that now is better than discovering it at the final account.
Interested in going further?
Contract type is chosen once and governs every conversation afterwards, which is why habit is an expensive way to choose it. Omega's PMP® Exam Preparation works through procurement and contracting as risk allocation decisions.
Contracting approaches and their risk implications appear in the appendices of the PMBOK® Guide Eighth Edition.
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References
A245: Make or Buy? How to Decide Before Procurement Begins
A246: Procurement Strategy: Decide How You Will Buy Before You Go to Market
A247: RFP vs RFQ vs IFB vs ITT: Which Procurement Document Should You Use?
A248: Choosing a Supplier: Cheapest Is Not the Same as Best
A250: Outcome-Based Contracts: Buying Results Rather Than Activity
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