What is CAC (customer acquisition cost)?

Blended and paid CAC

Two numbers, both useful, routinely confused.

Blended CAC divides all acquisition spend by all new customers, including those who arrived organically. It tells you what growth costs the business overall.

Paid CAC divides paid spend by customers attributable to paid. It tells you what the paid channels are doing.

Blended CAC flatters you when word of mouth is strong; paid CAC is what should govern channel decisions. Quoting one while a listener assumes the other is the most common way CAC gets misused in a board meeting.

What belongs in the numerator

• Media spend, always.
• Creative and production, which on small budgets can exceed media.
• Agency and platform fees.
• Sales costs where sales is part of acquisition — for B2B this often dominates.
• Marketing salaries, at least in any figure used to compare against LTV.

Using it properly

CAC alone decides nothing. It becomes meaningful against LTV, as a ratio and as a payback period.

It should also be computed per channel and per cohort. An account-level CAC averages a cheap channel that produces poor customers with an expensive one that produces good ones, and the average recommends nothing. And CAC rises as you scale — the cheapest audiences are exhausted first — so a target set at small volume will not survive growth.

The attribution problem

Paid CAC depends on knowing which customers came from paid, which is exactly what attribution has become worse at. Where AI assistant influence drives customers who arrive as direct or organic, paid CAC is overstated and blended CAC is correct — the customers exist, they are simply credited to nobody.

That makes blended CAC the more honest headline number in an environment with growing unattributable influence, and it makes an incrementality test the only way to split it back out reliably.