An add-on acquisition (also called a bolt-on) is a smaller company bought by an existing portfolio company, the platform, rather than by the fund directly. The platform supplies the management team, systems, and infrastructure; the add-on plugs into that base. Stacking several add-ons onto one platform is the mechanics of a buy-and-build.
Why it matters
Add-ons are the engine of a buy-and-build strategy. They grow the platform, often at a lower multiple than the platform itself, which blends down the average entry price and can drive multiple arbitrage at exit. They are also one of the more reliable ways to earn multiple expansion, because a larger, more diversified business generally commands a higher exit multiple than the small companies that were folded into it.
Blending down the entry multiple
Suppose the platform was bought at 6.0x and two add-ons are acquired at 4.5x each. The combined business carries a blended entry multiple below 6.0x. If the larger, integrated company then exits at 7.0x, the sponsor captures both the operating growth and the spread between the blended entry multiple and the higher exit multiple.
Where it fits
Add-ons are a core part of the operational and strategic side of value creation. Done well, they compound: each acquisition adds earnings, spreads fixed costs, and moves the platform up the size and quality curve that buyers pay more for. Done carelessly, integration risk and overpaying for the next deal can erase the arbitrage, which is why add-on discipline is its own underwriting exercise.