Everyone tracks CAC. Cost to acquire a new customer. It's table stakes — if you don't know what it costs to bring in a new logo, you can't make rational decisions about where to invest in growth.
But here's the number almost nobody tracks, and it's the one that matters more: Revenue Acquisition Cost.
RAC is the cost to acquire a dollar of revenue from your existing customer base. Expansion, upsell, cross-sell — what does it actually cost to move a customer from $10K to $20K? From $20K to $50K?
When you run that math honestly, a few things become very clear very fast.
First: RAC is almost always dramatically lower than CAC. You've already done the qualification work. The relationship exists. The trust is established. The data is there. You know what this customer does, what they care about, and what their next problem looks like. Selling into that context is fundamentally different from selling cold.
Second: most companies have no idea what their RAC is, because they don't treat expansion as something you have to acquire. They treat it as a natural outcome — customers grow because they're happy, and if they're not growing, that's the customer's fault for not seeing the value.
That framing is why 10-15x LTV potential sits uncaptured at most companies.
Expansion revenue doesn't just happen because a customer is satisfied. Satisfied customers don't automatically buy more. They need a motion — a pipeline with signals, milestones, and plays. They need someone asking the question. They need the opportunity surfaced at the right moment with the right framing.
RAC forces you to take expansion seriously as an investment. When you're tracking what it costs to acquire expansion revenue, you start asking: what's the motion that produces it? Who's running it? How do we make it more efficient?
And then you start to see the compounding returns that make your existing customer base worth more than your entire new logo pipeline.
Track CAC. That's the price of entering the game.
Track RAC. That's how you know if you're winning it.
Lincoln Murphy formally named and popularized Customer Success starting in 2010 and has spent 15 years connecting it to expansion revenue and commercial outcomes. Read The Premise.