Investment banker fees on sell side M&A

Boutique investment banker fees are one of the least transparent parts of the M&A industry. A founder hires a banker, signs a fee letter that says "5% success fee," and assumes the math is simple. It rarely is.

Real fee structures include retainers, tiered success fees, tail provisions, breakup fees, expense reimbursement, and sometimes equity participation. The headline percentage is one piece of a multi part economic model. Two firms quoting the same headline can produce materially different actual outcomes for the seller.

This piece breaks down what boutique investment banker fees actually look like in 2026, what's normal versus what's a red flag in an engagement letter, and how a founder evaluating multiple bankers should compare offers.

The five components of a sell side fee structure

1. Retainer (engagement fee)

A monthly or upfront fee paid regardless of deal outcome. Compensates the banker for the work done in pre sale planning, marketing, and managing the process. Typically $25,000 to $100,000 total over the engagement period for lower middle market deals. Retainers are credited against the success fee at close.

2. Success fee

The percentage of deal value the banker earns at close. The structure varies:

• Flat percentage (e.g., 5% of total deal value)
• Lehman formula: 5% on first $1M, 4% on next $1M, 3% on next $1M, 2% on next $1M, 1% on remainder
• Modified Lehman: tiered with different cutoffs based on the deal size
• Double Lehman: 10% on first $1M, 8% on next $1M, etc. (more common for smaller deals)

For lower middle market deals ($5M to $250M), modified Lehman or flat percentage between 1.5% and 5% is typical. Smaller deals get higher percentages.

3. Tail provision

After the engagement ends (whether closed or terminated), the banker is still owed a fee if the seller closes a deal with any buyer the banker introduced. Tail periods of 12 to 24 months are standard. Some banker fee letters include broader tail definitions ("any deal with any buyer the banker introduced" vs "the buyer the banker is actively in late stage discussions with").

4. Breakup fee or termination fee

Owed by either party if the engagement terminates without a closed deal. Bankers want a fee if the seller terminates unilaterally. Sellers want a fee if the banker walks away or fails to perform.

5. Expense reimbursement

Out of pocket costs the banker incurs (legal, accounting, travel, virtual data room, marketing materials). Typically reimbursed at cost. Caps of $25,000 to $50,000 are common.

What's normal versus what's a red flag

The math on a $50M deal

Three example fee structures, all on the same hypothetical $50M sell side deal:

Structure A: Flat 4% success fee, $50K retainer

• Retainer: $50,000 (credited)
• Success fee on $50M deal value: $2,000,000
• Less retainer credit: $50,000
• Net banker fee: $2,000,000

Structure B: Modified Lehman (5/4/3/2/1), $50K retainer

• 5% on first $1M = $50,000
• 4% on next $1M = $40,000
• 3% on next $1M = $30,000
• 2% on next $1M = $20,000
• 1% on remaining $46M = $460,000
• Total success fee: $600,000
• Less retainer credit: $50,000
• Net banker fee: $600,000

Structure C: Double Lehman (10/8/6/4/2), $25K retainer

• 10% on first $1M = $100,000
• 8% on next $1M = $80,000
• 6% on next $1M = $60,000
• 4% on next $1M = $40,000
• 2% on remaining $46M = $920,000
• Total success fee: $1,200,000
• Less retainer credit: $25,000
• Net banker fee: $1,200,000

Same deal, three different fee structures. The flat 4% costs the seller $2,000,000. The modified Lehman costs $600,000. The double Lehman costs $1,200,000. Spread of $1.4M on the same deal.

The Lehman formula was designed for smaller deals where the per dollar value of the banker's work is higher on the first $1M to $5M. On a $50M deal, the modified Lehman heavily favors the seller. On a $5M deal, the modified Lehman heavily favors the banker.

Founder evaluation framework

Three questions a founder should answer before signing any banker engagement letter:

Question 1: What's the all in banker fee on my expected deal value?

Run the math. Compare fee structures across 2 to 4 bankers you're seriously considering. Use the same expected deal value across all of them. The headline percentage doesn't tell the story; the math does.

Question 2: What's the tail provision and how is "buyer introduction" defined?

A 24 month tail with broad "any buyer ever discussed" language can come back to bite you years later. Negotiate the tail period and the definition of who counts as an introduced buyer.

Question 3: What happens if the deal doesn't close?

Some structures favor the banker (termination fees if the seller walks). Some favor the seller (banker continues to work on a contingency basis). Understand the downside before signing.

The broker dealer question

Some boutique firms operate as registered broker dealers. Some operate as M&A advisors only (no securities involvement). The distinction matters:

Registered broker dealers can handle deals that involve securities (stock for stock transactions, complex financing structures, certain types of recapitalizations). They're regulated by FINRA. Their fees can be paid out of seller proceeds at close.

M&A advisors without broker dealer registration can advise on asset purchases and certain business sale structures. They cannot accept transaction based compensation on securities deals. The fee structures and what they can do are limited.

For most lower middle market sell side deals (asset purchases, single buyer auctions), the distinction doesn't change much. For complex deals (cross border, recapitalizations, public to private), broker dealer status matters.

A founder should ask: "Are you a registered broker dealer?" If yes, the FINRA registration number should be public. If no, ask why not, what limits this places on what they can do, and how they handle compensation.

Industry benchmarks

Firmex's annual M&A Fee Guide is the closest thing to public benchmark data on banker fees in the lower middle market. It surveys 450+ M&A advisors across multiple regions and tracks fee structure trends year over year.

Recent Firmex Fee Guide findings include:

• Most middle market firms didn't raise fees in 2024 (only 34% of firms raised at least one fee category, down from 47% the prior year)
• Tiered (Lehman variant) success fees are more common than flat percentages on deals above $25M
• Retainers have been creeping upward as deal timelines extend
• Breakup fees are increasingly common in engagement letters

The Fee Guide is published in Global, North American, US, European, and DACH editions and is free to download from firmex.com.

The conversation to have before signing

A founder who is hiring a banker for the first time should run a structured comparison. Three to four banker meetings, same questions across all of them, side by side comparison of fee letters before deciding.

Questions to ask in those meetings:

• What's your typical fee structure on a deal my size?
• What's your retainer? Is it credited against success fee?
• What's your success fee? Walk me through the math on my expected deal value.
• What's the tail provision?
• What happens if I terminate? What happens if you walk away?
• Are you a registered broker dealer? FINRA number?
• What's your closed deal track record in my sector and at my deal size?
• Can I see anonymized examples of your last 3 engagements (deal size, multiple, process duration)?

Bankers who give clear, direct answers to these questions are easier to work with. Bankers who hedge or change subjects are harder to work with later.

Where to read next

For the timeline that frames where the banker engagement letter conversation happens in the broader sell side process, see The Sell Side M&A Process: 26 Week Timeline. For the LOI terms that the banker will negotiate on the founder's behalf with top buyers, see LOI and Exclusivity in Lower Middle Market M&A. For the founder landing page with full context on how LockRoom supports founder led sell side processes, see Founders.