6.4 Supplier Reimbursement Methods
Key Takeaways
- Fixed price transfers cost risk to the supplier and needs a well-defined scope; it is expensive and adversarial when requirements are still moving.
- Cost plus fee leaves cost risk with the buyer and suits genuinely undefined work, so it demands strong cost control, open-book records, and active supervision.
- Per unit quantity suits repetitive work where the method is known but the final quantity is not, pricing a rate rather than a total.
- Target cost shares the difference between target and actual cost through a pain/gain mechanism, aligning both parties to reduce out-turn cost.
- Choose the method by asking who carries cost risk, what behaviour it rewards, and how well the scope can be defined before contract award.
The second half of outcome 5c requires you to understand why different methods of supplier reimbursement are used and when it is appropriate to use them, and the syllabus names four: fixed price, cost plus fee, per unit quantity, and target cost. Learn all four by the same three tests — who carries cost risk, what the supplier is incentivised to do, and what the buyer must be able to define up front.
Supplier reimbursement methods
Reimbursement method (payment/pricing mechanism) determines how the supplier is paid and, critically, who bears cost risk when reality differs from the estimate. The syllabus expects fixed price, cost plus fee, per unit quantity, and target cost, with appropriateness by context.
Comparison table (risk and fit)
| Method | How payment works | Who bears most cost risk | When appropriate | When weak |
|---|---|---|---|---|
| Fixed price | Agreed lump sum (or fixed schedule of prices for a defined scope) for completing defined deliverables | Supplier (for cost of delivery within the defined scope) | Scope and risks are well understood; buyer wants cost certainty; competition is effective | High uncertainty, incomplete design, or buyer-caused change — leads to large variations or contingency padding |
| Cost plus fee | Allowable actual costs reimbursed + fee (%, fixed, or incentive-linked) | Buyer for cost of work (fee structure may add incentives) | Early design, emergency works, R&D, or when scope cannot yet be fixed | Weak cost control, open-ended scope, or poor audit of "allowable" costs |
| Per unit quantity | Agreed rate × measured quantity of units (m, m², hours, items) | Shared / situational — rate risk often with supplier; quantity risk often with buyer | Repetitive measurable work with uncertain final volume (earthworks, cable metres, call-off hours) | Hard-to-measure units, changing methods, or quality-not-quantity driven outcomes |
| Target cost | Target agreed; actual cost compared; pain/gain share splits under/over-runs per formula | Shared according to pain/gain share | Complex work with residual uncertainty but enough definition to set a meaningful target; collaboration desired | Unrealistic targets, weak open-book culture, or share formula that destroys supplier viability |
Terminology note: "Fixed price" is sometimes called lump sum. "Cost plus fee" may appear as cost-reimbursable. "Per unit quantity" aligns with unit-rate or remeasurement ideas. "Target cost" is often linked to pain/gain or target-cost incentive contracts. Use the syllabus labels in answers, then explain mechanism and risk.
Fixed price — deep dive
Under fixed price, the supplier commits to deliver the defined scope for an agreed price. If the supplier's costs rise because of inefficient delivery or mis-estimate, the supplier usually absorbs the overrun (subject to contract terms on client change, force majeure, and so on). The buyer gains budget predictability for that package.
Appropriate when:
- Requirements and interfaces are clear
- Design is sufficiently complete
- Risks the supplier can control are transferred deliberately
- Competitive market can price without extreme contingency
Not appropriate when: drawings are conceptual only, ground conditions are unknown and unallocated, or the buyer expects continuous scope evolution without change control. Suppliers then load contingency into the price or claim aggressively later.
PM judgement: fixed price does not mean "no change ever." Client-instructed changes still adjust price through change control. Fixed price means the baseline defined scope is priced as a commitment.
Cost plus fee — deep dive
Under cost plus fee, the buyer reimburses allowable costs (labour, materials, agreed overheads as defined) and pays a fee for profit and sometimes management. Cost risk of the work largely sits with the buyer; the supplier is less exposed to estimate error but may have less natural incentive to minimise cost unless the fee is structured to reward efficiency.
Appropriate when:
- Scope cannot be fixed (emergency repair, discovery work, early design assistance)
- Speed of start outweighs price certainty
- Trust, audit rights, and open-book processes exist
- The organisation can staff commercial control of timesheets, rates, and waste
Not appropriate when: the buyer wants a firm out-turn price, audit capacity is weak, or the work is routine and fully specified — then fixed price or unit rates usually give better value pressure.
Control essentials: define allowable costs, set fee type, require forecasts of out-turn, audit rights, and stage limits of financial authority for continuing reimbursable work.
Per unit quantity — deep dive
Per unit quantity payment multiplies an agreed unit rate by the measured quantity of completed units. Examples: £X per cubic metre of excavation, £Y per software test case executed (if defined carefully), £Z per training day delivered.
Risk pattern:
- Rate risk (productivity, method, input prices within the rate) often sits mainly with the supplier once the rate is agreed
- Quantity risk (how many units are needed) often sits with the buyer or the project need
Appropriate when: units are objectively measurable, method is understood, and total volume is uncertain at award. Civil remeasurement, cable installation, or bulk commodities often fit.
Not appropriate when: "units" are subjective, quality is non-linear with quantity, or suppliers can game measurement definitions. Always define measurement rules in the contract.
Target cost — deep dive
A target cost sets an agreed target for the out-turn cost of a defined scope. Actual allowable cost is compared to the target:
- Underrun (gain): buyer and supplier share the saving per an agreed formula
- Overrun (pain): both share the extra cost per formula (often with caps)
This shares cost risk and aims to align incentives: the supplier benefits from efficiency; the buyer retains a stake in outcomes and usually still runs open-book transparency.
Appropriate when:
- Work is complex but a realistic target can be set (often after some design maturity)
- Parties will genuinely collaborate and share information
- Pain/gain shares are fair and do not encourage unsafe cost cutting
Not appropriate when: the target is a fiction, culture is adversarial, or measurement of actual cost is unreliable. A bad target cost becomes a disguised dispute.
Worked comparison on one package
A data-centre client needs raised-floor installation. Design is complete; quantities are take-offable; market is competitive → fixed price or unit rates for m² with a firm quantity risk allocation.
Same client needs investigation of an unknown contamination plume before final remediation design → early cost plus fee investigation, then re-compete or convert remediation to fixed price or target cost once scope is clearer.
A five-year campus works programme with many similar small packages → framework relationship with call-offs using unit rates or mini-competed fixed prices.
A complex MEP integration with residual design risk but a mature cost plan → target cost with pain/gain to keep designer, installer, and client aligned.
Risk allocation summary for exam memory
| If the scenario shows… | Lean toward… |
|---|---|
| Clear scope, buyer wants certainty | Fixed price |
| Undefined scope, emergency or discovery | Cost plus fee (with strong controls) |
| Measurable repetitive units, uncertain volume | Per unit quantity |
| Complex shared risk, collaborative culture, settable target | Target cost |
| Many similar future packages | Framework / call-off relationship |
| Novel joint design over years | Partnering features + suitable reimbursement |
PMQ-style judgement scenarios
Scenario A — incomplete design, fixed-price pressure. A sponsor demands a fixed-price build contract on 30% design to "lock the budget." The PM should explain that suppliers will either refuse, load heavy contingency, or claim extensively. Recommend completing more design, using a two-stage approach, cost-plus for early works, or target cost with open book — and escalate the budget-certainty myth to the sponsor with options.
Scenario B — unit rates without measurement rules. A contractor is paid per metre of cable but "metre" is undefined (route length vs drum length vs including waste). Dispute follows. Remedy: define measurement and inclusion rules in the contract; do not rely on goodwill.
Scenario C — cost-plus without audit. Actual costs climb; fee is a percentage of cost, so the supplier earns more as spend rises. The PM should renegotiate fee structure where possible, impose forecasts and caps via change control, increase audit, and consider converting remaining work to target or fixed price once scope stabilises.
Scenario D — target cost with unfair share. A 90/10 pain share against the supplier for all overruns above a tight target may push the supplier into defensive behaviour or insolvency risk. Fair shares and realistic targets support Win-Win delivery behaviour.
Linking relationships and reimbursement
Do not choose mechanisms in isolation:
- Specify what you know; do not pretend certainty you lack.
- Allocate each major risk to the party best able to manage it — and pay accordingly.
- Match relationship intensity to uncertainty and duration.
- Keep governance: award, variations, and reimbursable spend still respect financial authority.
- In long responses: name method → state who holds cost risk → justify with scenario facts → note control measures (change control, audit, measurement rules, pain/gain).
That pattern answers APM PMQ procurement judgement questions with professional, applied reasoning rather than a single memorised "best contract" slogan.
When is a fixed-price reimbursement method usually most appropriate?
Under a cost-plus-fee arrangement, which statement best describes cost risk and control?
A project needs repetitive excavation where the method is understood but the final volume is uncertain until site work proceeds. Which reimbursement approach is usually the best fit?