Cost-plus or fixed fee: pricing a consulting job
When a consultancy should agree a cost-plus fee instead of a fixed fee, the four cost-plus structures, and a quick test for choosing the basis.
By Achekam · · 5 min read · For Consulting businesses in South Africa, Nigeria, Kenya
A prospective client wants a price for an investigation into why its distribution costs have doubled. Nobody knows yet whether the answer lies in one depot or in all of them, whether the data is clean or will need weeks of rebuilding, or how many interviews it will take. The client still wants a number on paper by Friday.
This is the moment a consultancy chooses how it will be paid, and the choice decides who carries the risk of the unknown. Quote a fixed fee and the firm absorbs every surprise. Agree to be reimbursed for costs plus a fee and the client absorbs them, but the firm takes on the work of proving every cost. Neither is right for every assignment.
Two ways to agree a price
Investopedia's explainer on cost-plus contracts sets out the distinction clearly. In a cost-plus, or cost-reimbursement, contract the project owner reimburses the contractor's expenses plus an additional profit, usually stated as a percentage of the contract price. A fixed-cost contract, by contrast, is agreed up front regardless of what the work actually costs.
For a consultancy, "expenses" mean more than travel and printing. They include the time of the consultants on the job, any subcontracted specialists, data purchases and field costs. On a fixed fee, all of that is the firm's problem once the price is signed. On a cost-plus basis, all of it is billable, provided the firm can show it was incurred.
When the scope cannot be estimated
Investopedia says cost-plus contracts are generally used when the party drawing up the contract has budgetary restrictions or when the scope cannot be properly estimated in advance. It adds a condition that matters a great deal in practice: all direct and indirect costs claimed must be supported by invoices and receipts.
Typical consulting work where the scope genuinely cannot be pinned down includes:
- forensic or fraud investigations, where each finding opens the next line of enquiry;
- turnaround work, where the depth of the problem only shows once the team is inside;
- research assignments whose sample depends on early results;
- system migrations where the state of the old data is unknown.
Work with a well-understood shape, such as a standard policy review, a defined training programme or a valuation with a known scope, usually suits a fixed fee better, because the firm can estimate it and the client values certainty.
Four cost-plus structures
Investopedia describes four kinds of cost-plus contract. In broad terms:
| Structure | How the fee element behaves |
|---|---|
| Cost-plus award fee | Part of the fee depends on how the client judges the work |
| Cost-plus fixed fee | Costs are reimbursed and the fee is set at the outset |
| Cost-plus incentive fee | The fee moves with agreed targets, such as finishing within an estimate |
| Cost-plus percent-of-cost | The fee is a percentage of cost, so reimbursement rises as costs rise |
The last of these is the one clients distrust most, for an obvious reason: the more the consultancy spends, the more it earns. A cost-plus fixed fee answers that concern, because the firm's profit stays the same however long the work takes.
Investopedia also lists the drawbacks of cost-plus generally: an uncertain final cost, typically a higher total cost, disputes over recovering expenses and the work of justifying all costs. It notes that cost-plus contracts normally do not cover contractor error or negligence, which is why some contracts cap the amount reimbursed. If the client proposes a cap, agree in writing what happens to work still needed once it is reached.
Why public buyers may prefer cost-plus
Investopedia says governments generally prefer cost-plus contracts because they can choose the most qualified contractor instead of the lowest bidder. It also names the matching risk for any owner: the contractor manipulating expenses.
So a consultancy winning cost-plus work from a public body, a donor-funded programme or a large corporate should expect its costs to be examined line by line. Before signing, agree:
- which costs are reimbursable, and which are covered by the fee;
- how consultants' time is recorded and at what rate it is charged;
- what evidence supports each claim: timesheets, supplier invoices, receipts;
- how often the firm may invoice, and what the client may query.
If the firm cannot produce that evidence quickly at month end, a cost-plus contract will cost it more in disputes than it gains in protection.
Quoting and invoicing either basis in Achekam
Whichever basis you agree, the quote and the invoice need to match it.
In Achekam, a quotation or proposal carries one VAT rate for the whole document, by default the approved standard rate for the business's country. A cost-plus quote that mixes items at different VAT rates cannot show them line by line on one document, so state the fee basis and the treatment of each kind of cost in the engagement terms themselves.
There is also a current gap to plan around. A business cannot yet save a plain sales quote and later turn it into an invoice: quotes on the Billing & Finance and Smart Accounting pages live only in the browser and are lost on reload. Until that changes, keep the signed quote or agreement on file outside those pages.
Invoices are on firmer ground. A business creates customer invoices as drafts it can change or delete, and issuing one takes the next number in its sequence and posts it to the ledger as debtors, sales and output VAT. For a cost-plus job, build the month's draft from the timesheets and supplier invoices, check it against the reimbursable list, then issue it. Default terms are 30 days; change them if the contract says otherwise. Work done but not yet billed at month end is covered in unbilled work at month end, and reporting fees by type of work in fee income by service line.
A short test for choosing the fee basis
Ask four questions before you price:
- Can we describe the deliverable precisely? If yes, lean towards a fixed fee.
- Would a fair estimate have a wide range? If yes, cost-plus, or a fixed fee for a first phase only.
- Can we evidence every cost by invoice, receipt or timesheet each month? If not, do not offer cost-plus yet.
- Does the client need a ceiling? Then agree a cap and what happens beyond it.
For the distribution-cost investigation, a sensible answer might be a fixed fee for a short diagnostic phase, followed by a cost-plus fixed fee for the work the diagnosis uncovers. Write the basis into the engagement terms before any work starts.
General guidance only, not advice on your own circumstances. Tax and payroll rules change: check the current position with the authority or your adviser.
