Shadow billing is the seller’s second invoice. The one the buyer never agreed to.

What shadow billing actually is.

Shadow billing is everything the buyer is charged for that does not appear as a named line in the service catalog. The catalog lists IT support, payroll processing, finance close support, procurement, and the agreed monthly fees. The shadow ledger contains everything else. Travel time charged at a fully loaded rate. Project labor coded under a generic engineering bucket. Catch up adjustments for services delivered in months past. Allocations to overhead pools that the buyer never approved.

It is not always intentional. Sellers run their TSA invoicing through the same enterprise billing system that runs their internal cost recovery. Internal charges flow through naturally. The carve out invoice picks them up. The buyer receives a line called "shared services support" or "centralized operations" with no breakdown. The line gets paid. The cost sits on the buyer’s P&L. The catalog has nothing to say about it.

The aggregate impact is significant. Across multiple carve-outs, shadow billing runs from 3 to 8 percent of the total TSA cost. On a $20M annual TSA, that is $600K to $1.6M of unbudgeted charges per year. The number compounds when the TSA term extends beyond original plan.

The remedy is not a one time audit. It is a parallel ledger maintained by the buyer that tracks every committed charge against every actual charge. When the two diverge, the gap is shadow billing and a written query goes to the seller within the billing cycle.

The three channels shadow charges flow through.

The first channel is the catch all line. Names vary. "Other services." "Transition support." "Project allocation." The line aggregates dozens of charges that the seller’s billing system grouped together because there was no specific catalog item to assign them to. The buyer cannot pressure-test a single number without seeing the underlying detail. The detail rarely arrives unless the buyer demands it in writing.

The second channel is unbilled labor. The TSA contract specifies a fixed monthly fee for a workstream. Labor inside that fee is supposed to be unlimited within the agreed scope. The seller’s timekeeping system tracks every hour. Hours beyond the seller’s internal threshold convert to project labor and arrive on the invoice as a separate charge under a project code that was never approved.

The third channel is the allocation. The seller’s overhead pools, IT capital costs, real estate allocations, and shared services costs get distributed across business units. Carve out entities sometimes carry the same allocation rate as before separation even though most of the entitlement has stopped. The allocation appears as a single number with no transparent methodology.

All three channels have the same defense. The buyer demands the underlying detail before paying. If the detail does not tie to a catalog entry or an agreed pass-through, the charge becomes a written query against the invoice. The mechanism is the same as the TSA overcharge identification review, applied with extra discipline to the catch all lines.

The parallel ledger that catches the gap.

The buyer maintains a parallel ledger from Day One. Every catalog line gets its own monthly accrual. Fixed fees accrue at one twelfth of the annual number. Variable fees accrue based on the agreed volume and rate. Pass-through accrues based on the seller’s monthly billing run. The total parallel accrual is what the buyer expects the invoice to show.

When the invoice arrives, the actual is compared to the expected. Variance above 3 percent triggers a structured review. Variance above 5 percent triggers a written query. The query asks for the underlying detail of the variance line. The seller has 30 days to respond. Without a clear contractual basis tying the variance to a catalog entry, the buyer withholds the disputed portion pending resolution.

The parallel ledger does three things at once. It catches shadow billing as it appears. It builds the audit trail for any later dispute. It calibrates the buyer’s P&L forecast so that surprise costs do not blow through the operating budget. The discipline is more important than the tool. A spreadsheet runs it. The work is the comparison.

Most buyers do not maintain the ledger. The seller’s invoice gets paid because there is no internal alternative number to compare it against. Where the ledger does exist, recovery against shadow billing runs 60 to 80 percent of the contested amount. The work pays back in the first quarter.

Contract language that closes the channel.

Shadow billing is harder to execute when the contract closes the door on it before signing. Three clauses do the work. First, a positive scope statement that defines the catalog as the only source of permitted charges. Second, an explicit prohibition on overhead allocations that are not separately listed and priced. Third, a documentation requirement that any invoice line above a stated threshold must include underlying detail.

The positive scope statement is short. Charges permitted under this Agreement are limited to the services and prices stated in the Service Catalog. Any charge outside the Catalog requires prior written approval by the Buyer. The clause is one paragraph. It eliminates the entire shadow billing channel where it is properly drafted at the pre-signing stage. Most TSAs as initially drafted by the seller do not contain this clause.

The allocation prohibition is similarly short. No overhead, corporate allocation, or shared services charge shall be billed except as a named line in the Service Catalog with a stated methodology. This eliminates the silent allocation channel. The third clause around documentation forces transparency on the catch all lines. Any line above a stated dollar threshold must include the underlying transaction detail at invoice issuance.

These three clauses are routinely negotiated into the TSA before signing. They are not controversial. Most sellers accept them when they are raised with specific language. The leverage to insert them is the TSA pre-signing leverage window, which closes the moment definitive documents are signed.

What to do when the TSA is already signed.

When the TSA is already signed and the contract does not contain the closing clauses, the buyer runs detection rather than prevention. The first step is a baseline reconciliation against the first three months of invoicing. Every line is mapped to a catalog entry. Lines that do not map become flagged. The seller is asked to map them or remove them. Most resolve at this stage because the seller’s billing team also wants the invoice to be clean.

The second step is the catch all line discipline. Every catch all line gets a standing query that requests underlying detail. The buyer pays the catalog lines and withholds the catch all line pending detail. The seller usually provides the detail within one billing cycle. Where the detail reveals that the underlying charges are out of catalog, the credit is processed.

The third step is the formal change control. Where the seller has been billing shadow charges for several months and refuses to credit, the buyer raises the issue at the governance committee. Most resolve at committee. Where they do not, the formal dispute path is taken. The leverage in a dispute is the contract. If the contract does not authorize the charge, the buyer is not obligated to pay it.

A back end audit recovers some of the shadow billing that has already been paid. The recovery rate against a one time audit is lower than the recovery against a structured monthly review, but it is still meaningful. A typical engagement on a TSA that has been running for 12 months recovers 1 to 3 percent of total spend. The audit pays for itself in 30 days.

Why shadow billing survives most TSA reviews.

Shadow billing survives because the buyer’s default review pattern is wrong. The typical finance review checks that the invoice total matches the budget. It does not check whether each line ties to a contract entry. The line items get paid because they look reasonable. The catch all line gets paid because it is small relative to the total. Over 24 months, the small lines compound into a material number.

It survives because the buyer’s finance team does not have visibility into the catalog. The TSA contract sits with legal or with M&A integration. The invoice sits with accounts payable. The two functions rarely synchronize. The catalog is not embedded in the AP system. The invoice clears the standard approval workflow without anyone comparing it to the contract.

It survives because the seller has structural information advantage. The seller knows what the underlying activity costs. The seller controls the timekeeping, the allocation methodology, and the billing system. The buyer sees the output but not the inputs. Without forced transparency, the seller’s number is the only number on the table.

The fix is structural rather than tactical. The catalog goes into the AP system. The parallel ledger goes onto the finance team’s monthly close. The TSA contract reviewer sits in the same room as the AP approver once a month. The work is administrative. The savings are substantial. The annual TSA true-up management exercise is where the work closes out at year end.

More on TSA cost reduction.