Definition
The full cost of winning one new customer (advertising, agency fees, sales time, the software in between) divided by the customers actually won. Compared against lifetime value, it is the core unit-economics ratio: a healthy business earns back what it spent well inside the customer relationship.
What it looks like in practice
A med spa owner tallies one month of getting found: the ad budget, the retainer for whoever manages it, the booking software, and the hours her front desk spends returning inquiry calls and rebooking no-shows. All of it counts, not just the ads. Divide the total by the number of first-time clients who actually walked in that month and she has her acquisition cost. The number is uncomfortable until she checks the other side; leads that were called back the same day converted; the ones left in the voicemail box did not. Her cost per client is mostly a follow-up problem.
Why it matters
Knowing what a customer actually costs to win is what separates marketing spend that builds the business from spend that quietly drains it. The figure only means something next to lifetime value; paying well to acquire customers who never come back grows revenue and loses money at the same time. Two things distort it. Owners routinely leave out their own time and their staff's, which makes the number look better than it is. And spend takes weeks to show up as customers, so a month-by-month reading swings wildly. Watch it as a trend against lifetime value, and fix leaks before buying more leads.