What is the Double Lehman formula that is used for M&A fee structure?

The Double Lehman formula is a stepped success-fee schedule that M&A advisors use as a starting point on mid-market deals. It comes from the original Lehman formula (5-4-3-2-1) that Lehman Brothers used in the 1960s and 1970s. The name is not one scale. The common Double Lehman doubles those rates to 10-8-6-4-2. Mid-market shops also use a 10-9-8-7-6 schedule that then steps to 5% and 4%. On that mid-market schedule, a $5 million deal is a blended 8% ($400,000) and a $20 million deal is a blended 5.25% ($1.05 million). The engagement letter sets the fee.