The earnout is the most feared component of a deal and the most misunderstood. Buyers either over-rely on it (treating it as free financing) or avoid it (fearing the dispute). The truth sits between: an earnout is a risk-sharing instrument with a known hit rate, and once you underwrite it at its real expected value and define it tightly enough to stay out of court, it becomes one of the most useful tools for bridging a valuation gap on a book whose retention is genuinely uncertain.
§ 01 · Underwrite at 50%The hit rate that reframes it.
Approximately half of earnouts hit their base target — so the buyer's planning assumption should be a 50% payout, not 100%. A $3M headline deal with a $900K earnout is a $2.55M expected-value deal. Underwrite at expected value, and the earnout stops being a price you fear and becomes a risk you've priced.
The single most clarifying fact about earnouts is the hit rate: roughly 50% of earnouts hit their base target. That means the buyer's planning assumption should be a 50% payout, not the 100% a nervous buyer fears or the 0% a hopeful one bets on. Run the math at expected value: a $3M headline deal with a $900K earnout at 50% probability is a $2.55M expected-value deal. Underwriting at expected value reframes the whole instrument — the earnout isn't a price hanging over the deal, it's a probabilistically-weighted component you've already priced. That's the same present-value discipline the vanity-versus-sanity framework applies across every component, and it's why the earnout discounts to 30–60% of face: the 50% hit rate, layered with measurement and counterparty risk and time value.
§ 02 · Pick the right metricWhy retention is the gold standard.
| Earnout metric | Usage | Why |
|---|---|---|
| Revenue | ~65% | Objective, hard to manipulate |
| EBITDA | ~17% | Down — buyer-side cost-allocation fights |
| Retention | Gold standard for books | System data, tied to what you're buying |
The metric you choose decides whether the earnout pays cleanly or ends in a fight. Modern agency earnouts use revenue 65% of the time and EBITDA only 17% — EBITDA usage has fallen because the buyer controls cost allocation post-close, which makes the number manipulable and the earnout a magnet for disputes. For a book purchase, retention is the gold standard: it's objective (drawn straight from system data), tied directly to what the buyer is paying for, and hard for either side to manipulate. A retention earnout structures one of two ways — a cliff (all-or-nothing at a threshold, say 85%) or a sliding scale (linear from a floor to a ceiling) — and a whale-client earnout isolates the retention of a single concentrated top client as its own condition, which is essential when one client drives a material slice of revenue. Pair a revenue earnout with retention guardrails — a minimum 88% book retention, a cap on new-client contribution, one-time revenue excluded — so the seller can't hit a revenue target while the book quietly churns underneath. The retention assumption all of this protects is the same one valued in the pro-forma EBITDA framework.
§ 03 · Size and time it20–30% over 12 months.
Sizing and timing follow from the role the earnout plays. Size it at 20–30% of purchase price in sub-$5M deals: below 20% doesn't motivate the seller to support retention, and above 30% transfers too much valuation risk to them, which either kills the deal or invites the seller to game the metric. Measure over 12 months — one full renewal cycle — as the most common period; 24 months appears on higher-risk books, and 36 months is rare and operationally friction-heavy (a long earnout means a long stretch where the buyer can't freely run the business). The measurement period is itself a structural choice: it has to be long enough for one renewal cycle to prove retention, but short enough that the buyer regains operational freedom quickly. Get the size and the window right and the earnout motivates the seller to help retain the book through its first renewal — which is exactly the behavior the buyer is paying for. The legal mechanics of drafting these terms are in drafting the earnout.
§ 04 · Keep it out of courtThe 85% dispute-free structure.
An earnout's worst outcome isn't a missed target — it's a lawsuit over whether the target was missed. The good news is that disputes are largely preventable: deals with explicit metric definitions, specific negative covenants (commitments by the buyer not to take actions that would suppress the metric — no punitive cost allocations, no starving the book of service), and a bifurcated dispute-resolution mechanism reach resolution without litigation 85% of the time. The discipline is to define everything that can be defined before signing: how the metric is calculated, what's included and excluded, who measures it and on what data, what happens if the parties disagree, and what the buyer is and isn't allowed to do during the period. Vague earnouts produce litigation; detailed ones produce payments. Underwrite at 50%, choose retention as the metric, size it at 20–30% over 12 months, and define it tightly enough to stay out of court — do those four things and the earnout becomes the precise risk-sharing tool it was meant to be, not the dispute everyone fears. How the earnout sits within the full layered structure is covered in hybrid deal structures.
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Terminology on this shelf
- Earnout hit rate
- ~50% of earnouts hit their base target — the buyer's planning assumption, not 100%.
- Retention earnout
- The gold standard for book purchases — objective, system-sourced, tied to what's being bought.
- Cliff vs sliding scale
- All-or-nothing at a threshold, versus linear payment from a floor to a ceiling.
- Whale-client earnout
- Isolating a single concentrated top client's retention as its own earnout condition.
- Revenue-quality guardrails
- Minimum book retention, capped new-client contribution, one-time revenue excluded.
- Specific negative covenants
- Buyer commitments not to suppress the metric — the backbone of the 85% dispute-free rate.