Client attrition — the transition scenario sets the number.

Client attrition is the most consequential single adjustment in a synergy pro-forma, and the most commonly mishandled — buyers model it as a single point estimate when it's actually a range whose value the deal structure determines. The same book loses about 5% of revenue under a well-structured transition and about 15% under a rushed one, and the buyer's modeling assumption has to follow the transition they actually negotiate. Get the link between structure and number right, and the attrition assumption becomes defensible rather than a guess.

§ 01 · Three transition scenariosThe number follows the structure.

Attrition is transition-structure-dependent, and three scenarios bracket it. A strong transition — the seller available 12+ months, making personal client introductions and actively facilitating the handoff — runs about 5%. A standard transition — the seller available 3–6 months with top-tier introductions and general availability — runs about 10%, and is the most common mid-market structure. A minimal transition — the seller exiting at or shortly after closing — runs about 15%. The buyer's model has to match the structure they actually have, which is why a single low estimate applied regardless of structure is systematically wrong. This maps directly to the risk-offset column of the synergy pro-forma, where the 5%/10%/15% applies to the target revenue baseline as one of the most consequential adjustments in the model.

§ 02 · Four driversAnd the one the buyer controls.

The four drivers are partially controllable, and the distinction matters for both modeling and execution. Relationship intensity is a fact about the book a buyer reads in diligence — a book heavily owned by the selling principal concentrates its transition risk around that principal's availability, while a producer-team-serviced book retains better regardless. Carrier continuity is partly a structural choice — keeping the same carrier, policy, and renewal lowers attrition, while a code merge or carrier change raises it. Geographic and cultural fit are largely given. But communication cadence is the lever fully within the buyer's control: clients who hear from the buyer quickly, with a clear message, retain dramatically better — which is why disciplined acquirers treat post-close communication as their single most important operational priority. The attrition number isn't purely fate; the buyer's execution moves it.

§ 03 · The modeling nuancesCount, revenue, and timing.

Two nuances separate an honest attrition model from a crude one. First, the count-versus-revenue asymmetry: 10% count-based attrition typically produces only 6%–8% revenue attrition, because smaller accounts churn faster than larger ones — so a buyer who applies a count-based rate to revenue overstates the loss, and modeling the distinction produces a more honest pro-forma. Second, the timing split: 70%–80% of attrition lands in year 1 and the remainder in year 2, with the acquired book retaining at the acquirer's baseline rate by year 3 — so the model front-loads the loss rather than spreading it evenly. The valuation stakes make the precision worth it: on a $1M revenue acquired book, the difference between a 5% and a 15% assumption is a $100K first-year revenue delta, which is $25K–$35K of first-year EBITDA and $150K–$250K of valuation at typical multiples — meaningful on any deal and decisive on a smaller one. Attrition is the pre-acquisition analogue of historical retention, the read on which is in leaky-bucket attrition.

§ 04 · The TSA and the caution ruleWhat earns the low number.

The structure-to-number link has a documentation requirement: a verbal seller commitment defaults to the minimal scenario in the buyer's model, regardless of the seller's actual intent, because the buyer can only underwrite what's enforceable. Earning strong-transition treatment requires a documented transition services agreement specifying the seller's post-close availability, the frequency and type of client communications, and any compensation arrangement — which creates the enforceable structure a buyer will model the low number against. This is also a seller's most practical lever: a 60–90 day structured transition, even by a seller who planned to exit at closing, often justifies a price bump that exceeds the value of walking away at close, because the arithmetic favors the brief structured engagement. The governing discipline is caution-beats-optimism: a deal falling between scenarios is modeled at the higher attrition number, because buyers who treat attrition as an afterthought bid competitively on deals that don't support the implied assumption and absorb the shortfall post-close. Model the structure you have, document it for the low number, and communicate relentlessly — that's how attrition becomes a managed adjustment rather than a post-close surprise.

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