What a Sell-Side Engagement Actually Costs on a $25M to $100M Deal

Most engagement letters a middle-market founder receives read like a form document. The retainer line, the success-fee schedule, the tail, the expense clause and the minimum fee are presented as a package, and the implicit message is that the terms are standard. On a $25 million to $100 million transaction they are not standard. They are a priced bundle, and the dollar swing between a well-negotiated letter and a poorly negotiated one on a deal in that range routinely runs into the mid-six figures.

What follows prices the full stack a seller actually pays on a sell-side engagement in that deal band, section by section, and flags which terms are genuinely negotiable before signing. It is informational, not legal or financial advice, and no two engagement letters are identical. The intent is to let a founder or CFO walk into a scoping conversation with concrete numbers rather than category averages from a general sell-side advisor overview.

The Retainer and Work Fee Are Pricing Commitment

On a $25M to $100M sell-side mandate, two retainer structures dominate. The first is an upfront engagement fee of roughly $25,000 to $100,000, paid at signing. The second is a monthly work fee of $10,000 to $25,000 that runs for the life of the engagement. Firmex's survey work describes the most common structure as a monthly work fee of $5,000 to $10,000 deducted from any success fee, with larger mandates sitting at the upper end of that band and higher.

Three things matter in the fine print. First, is the retainer creditable against the success fee, dollar for dollar, with no cap on the amount creditable. Second, is it refundable in any scenario (almost never, but ask). Third, is it capped in aggregate, or does a monthly fee run indefinitely if the process drags past 12 months. A monthly work fee without a cap is a different economic instrument from one that stops at month nine.

The shift toward monthly fees is not a boutique quirk. The Firmex guide reports that advisors have moved deliberately toward recurring revenue because deal timelines have extended and closing certainty has fallen. For a seller, this means the retainer line is not a negotiation about a few thousand dollars. It is a negotiation about who absorbs the risk of a slow process.

The Success Fee and Why the Formula Matters More Than the Percentage

Success fees in the $25M to $100M range typically fall between 1.5% and 5% of total consideration, with the blended rate declining as deal size rises. The Firmex 2024-25 guide puts the typical sell-side success fee at roughly 5.5% on a $5 million deal and about 2.0% on a $150 million deal. That decline is almost always implemented through a tiered formula rather than a single blended rate.

Three formulas dominate letters in this band:

• Flat percentage. A single rate, often 2% to 4%, applied to total consideration. Simplest to model, hardest to reverse-engineer once signed.
• Double Lehman. 10% on the first $1M, 8% on the second, 6% on the third, 4% on the fourth, and 2% on everything above $4M. On a $25M deal this blends to roughly 2.8%. On a $75M deal it blends closer to 1.6%.
• Modified Lehman with an escalator. A tiered scale that increases the marginal rate above a target price. A letter might pay 2% to the first $40M of consideration and 5% to 8% on every dollar above that. This is the single most important clause a seller can negotiate into the letter, because it aligns the advisor with price maximization rather than deal certainty.

The Firmex survey finds that the declining-rate Lehman structure is the most common sell-side success-fee framework among 51% of advisor respondents. The absolute percentage is less consequential than whether the marginal rate above the expected value rises or falls. A 2% flat fee on a $60M deal and a 1.5% base with a 10% escalator above $55M produce very different advisor behavior in the final two weeks of negotiation.

Minimum Fees Quietly Reprice Small Transactions

Nearly every engagement letter in this band carries a minimum success fee. On $25M to $100M mandates, minimums commonly fall between $400,000 and $1,000,000, scaled to the advisor's cost base and the complexity of the process. The minimum is irrelevant if the deal closes at or above the expected value. It becomes the dominant economic term if the process produces a lower-than-expected offer that the seller nonetheless accepts.

Consider a letter with a 2.5% success fee and a $750,000 minimum on a company the advisor positions at $40M. If the final transaction closes at $22M because of a diligence finding, the formula says the advisor earns $550,000. The minimum says $750,000. The seller pays the higher number. A reasonable negotiation point is a minimum that steps down proportionally if the deal closes materially below the pitched range, or a minimum that applies only to the base fee and not to any escalator.

The Tail Is Where Letters Go Sideways

The tail is the period after engagement termination during which the advisor still earns the full success fee if the seller closes with a buyer the advisor introduced. Standard tail periods run 12 to 24 months, and the advisor earns the full fee if the seller closes with a contact introduced during the engagement. Thompson Coburn's M&A counsel observe that banks commonly push for 18 to 24 months while six or nine months is usually sufficient from the client's perspective.

Three tail terms are negotiable and worth the effort:

1. Duration. Twelve months is defensible. Twenty-four months is not, absent an extended quiet period. Nine to twelve is where most negotiated letters land.
2. The buyer list. The tail should apply only to buyers on a written list the advisor delivers at termination, not to any party the advisor claims to have "contacted." Vague introductions are the single biggest post-engagement dispute source.
3. Credit against a replacement advisor. If the seller re-engages a different advisor who closes with a party on the tail list, the first advisor's fee should be reduced by what the new advisor earns, not stacked on top.

Sellers who are already thinking about tail coverage mechanics before closing tend to negotiate these points without friction. Sellers who have not thought about them often sign the stock language.

Expenses, Term Length and Termination Rights

Expenses are the easiest line to miss. Letters commonly reimburse the advisor for out-of-pocket costs, which can include travel, legal counsel to the advisor, printing and virtual data room costs. On a $25M to $100M process these frequently total $25,000 to $75,000. A reasonable negotiation is a monthly or aggregate expense cap above which the seller's prior written consent is required.

Term length and termination rights are the next layer. Engagement letters in this band typically run 6 to 12 months as an initial exclusive term, with the seller retaining the right to terminate without cause on 30 days' written notice. A letter that locks the seller in for 18 months with no termination right is a letter to walk away from.

Two further items belong on the diligence checklist. First, when is the success fee payable. Firmex reports that 57% of advisors expect full payment at closing while 43% defer the portion attributable to earnouts and seller financing until those contingent payments arrive. On a transaction with a material earnout component, deferring the fee tied to contingent consideration is both reasonable and increasingly common. Second, the fee base: total consideration should be defined to exclude assumed liabilities, transaction expenses and seller-funded escrows for a defined period.

What the Full Stack Actually Looks Like

Pricing a representative $50M sell-side engagement end to end: a $75,000 upfront retainer, a $15,000 monthly work fee for seven months ($105,000) both creditable against the success fee, a success fee of roughly $1.1M to $1.4M depending on the formula, a $600,000 to $800,000 minimum that does not bind at that outcome, reimbursed expenses of $40,000 to $60,000, and legal counsel to the seller running roughly $100,000 to $500,000 for a middle-market transaction. All-in advisor cost at a clean closing: approximately 2.5% to 3.2% of enterprise value, before legal and quality-of-earnings work.

Two numbers inside that stack move materially with negotiation. The escalator above the expected value, if any, can add or subtract $200,000 to $500,000 on the margin. The tail terms can create or eliminate a $1M-plus liability 18 months after the engagement ends. The retainer and expense lines, taken together, rarely move the all-in rate by more than 30 basis points.

What to Do With the Letter in Front of You

A term sheet in hand is a scoping conversation, not a signing ceremony. Three practical steps before counter-signing: model the success fee under at least two closing values, not just the pitched range; price the tail in dollars at a realistic post-engagement deal with a party already on the advisor's radar; and read the expense and indemnification clauses with the same attention as the success fee schedule. Sellers who do this work before signing tend to find that most of the terms described above are, in fact, negotiable. The ones that are not are usually disclosed early and priced into the rest of the letter.

The engagement letter is the first serious commercial document a seller signs in a sale process. Treated as a form, it tends to produce a form outcome. Treated as a priced bundle with named line items, it becomes the first place a disciplined seller recovers value that would otherwise leak out of the transaction.