Two models. One fits each service.

Cost-plus shifts risk to the buyer.

Cost-plus pricing places the cost variance risk on the buyer. The seller documents actual cost, applies the agreed mark-up, and invoices the result. If the cost rises because volumes increase, because allocated overhead changes, or because the seller's labor rates move, the invoice rises. The buyer has limited mechanisms to push back without auditing the underlying cost build-up.

The buyer who accepts cost-plus accepts three specific exposures. Volume movement, where activity above the assumed baseline produces a larger invoice. Cost escalation, where the seller's underlying labor or vendor costs rise during the TSA period. Allocation drift, where overhead pools or allocation methodologies shift in ways that increase the cost component without changing the underlying service.

Each of these exposures can be capped contractually. Volume caps limit the cost adjustment to a defined band. Cost escalation can be tied to a published index rather than the seller's discretion. Allocation methodology can be fixed at signing and locked for the TSA period. The buyer who negotiates these caps converts an open ended exposure into a managed one. The buyer who does not negotiate them carries the exposure.

Cost-plus is the right model when the cost base is genuinely variable and the buyer wants to pay for actual usage rather than a worst case fixed price. Application support, professional services, and variable infrastructure consumption are common fits. The buyer should require detailed cost documentation, audit rights, and the contractual caps that prevent open ended exposure.

Fixed-fee shifts risk to the seller.

Fixed-fee pricing places the cost variance risk on the seller. The seller invoices the same monthly amount regardless of cost movement, within an agreed volume band. The buyer pays a predictable price and the seller absorbs the operational variance. Fixed-fee removes the audit burden, simplifies governance, and produces clean monthly close.

The buyer pays a premium for that certainty. The fixed price typically includes a buffer that compensates the seller for absorbing the risk. The buffer varies by service, but it is real, and the buyer should expect it. The trade is certainty for cost. The buyer who values certainty pays the buffer happily. The buyer who values cost pays cost-plus and accepts the variance.

Fixed-fee fails when scope is poorly defined. The seller's view of what is included in the fixed price and the buyer's view diverge during the first month of operation. The resulting dispute consumes governance capacity and damages the working relationship. The remedy is detailed service descriptions, named exclusions, and a clear volume baseline. The discipline of writing these clearly is the discipline that makes fixed-fee fixed.

Fixed-fee fits services where the volume is predictable, the cost is stable, and the service description is well defined. Back office finance functions, payroll processing, accounts payable, help desk, and basic infrastructure are typical fits. For these services, the buyer should propose fixed-fee in the first redline, even if the seller's first draft proposes cost-plus.

The decision framework per service.

The pricing decision should be made service by service, not at the contract level. Each service in the catalog has a cost profile and a volume profile. The pricing model that fits depends on those profiles. A uniform cost-plus or uniform fixed-fee schedule is a sign that the catalog has not been examined carefully. A schedule that mixes both is a sign of disciplined work.

The decision framework asks four questions for each service. Is the volume predictable within a 25 percent band? Is the cost base stable, with no expected step changes during the TSA period? Is the service description well defined enough to write detailed exclusions? Does the buyer value monthly cost certainty more than potential variance to the upside? Three or four yes answers point to fixed-fee. Two or fewer point to cost-plus.

For services that sit in the middle, hybrid structures work. A fixed-fee base for the core service, with a per-unit rate for volumes outside the band. A cost-plus model with a fixed mark-up and capped allocation. Hybrids let the buyer pay fixed for the stable part and variable for the variable part. The complexity is worth it when the service has both a stable core and a variable tail.

The detailed mark-up benchmarks for cost-plus services are covered in TSA mark-up benchmarks. The negotiation posture and pricing redline strategy are covered in how to negotiate a TSA. The pricing schedule should be an exhibit to the TSA, not a paragraph in the body.

Failure modes of each model.

Cost-plus fails when the seller has discretion over cost components. Allocated overhead that the buyer cannot challenge. Labor categories where the seller decides what blended rate applies. Vendor pass-through that includes administrative add ons. Each of these is a documented pattern that converts cost-plus into a higher cost than the parties intended. The remedy is detailed contract language that limits seller discretion, not generic auditing.

Cost-plus also fails when the audit rights are weak. The buyer should have access to the underlying cost records on demand, not just to summary invoices. Without access, every dispute about an invoice line becomes a dispute about the documentation. With access, the dispute is about the numbers themselves, which is faster to resolve.

Fixed-fee fails when the volume baseline is wrong. If the contract assumes a certain volume and actual volume is materially higher or lower, the fixed-fee model breaks. The seller demands a price increase if volume is higher. The buyer demands a price reduction if volume is lower. Either dispute consumes governance capacity. The remedy is a clear volume baseline backed by documented historical data, with a defined tolerance band and a per-unit rate for volumes outside the band.

Fixed-fee also fails when the service scope is loosely defined. The seller's view of what is in scope and the buyer's view diverge, and the divergence becomes a dispute. The remedy is detailed service descriptions written at the level of named activities, named inputs, named outputs, and named exclusions. A page per service is the right length. A paragraph per service is the wrong length.

The buyer's posture in the redline.

The buyer's pricing redline should propose a pricing model for each service, with reasoning. Not just a counter to the seller's proposal, but a fresh proposal that reflects what the buyer wants the contract to look like. The seller's first draft sets one frame. The buyer's redline should set a different frame. The negotiation then runs between the two frames, not between the seller's draft and the buyer's silence.

For services the buyer wants fixed-fee, the redline should include the proposed fixed price, the volume baseline, the tolerance band, and the per-unit rate for variance. For services the buyer accepts as cost-plus, the redline should include the proposed mark-up, the cost component definition, the audit rights, and the allocation methodology. Specificity moves the conversation.

The trade structure matters. The seller may resist fixed-fee on services where it values the cost variance protection. The buyer may resist cost-plus on services where it values the cost certainty. Both sides can find acceptable middle ground if the trade is structured. Fixed-fee on three services in exchange for a higher mark-up on two services may be the right deal. The buyer who knows what trades are acceptable can negotiate efficiently.

The single most important posture is that the pricing redline is detailed and benchmark backed. A generic objection to the seller's pricing moves nothing. A specific counter with numbers, structure, and reasoning moves a lot. The pass-through patterns to watch are in TSA pass-through pricing. The market mark-up ranges to anchor the cost-plus discussion are in TSA mark-up benchmarks.

More on TSA negotiation.