What Is Blended CAC?
Blended customer acquisition cost is total marketing spend across all channels divided by total new customers acquired in the period. No per-channel attribution. Every customer counts in the denominator regardless of how the user-level attribution system would have credited their acquisition; every marketing dollar counts in the numerator regardless of which channel it was spent on.
Blended CAC is the metric of choice for brands that have rejected per-channel attribution as unreliable in the AI search era. Like MER, it sidesteps the attribution problem by not attributing.
Why Blended CAC Matters
Per-channel CAC (the channel's spend divided by the channel's attributed customers) is calculated using the channel's attribution model, which systematically undercredits dark-funnel and AI-influenced acquisition. Channels that look good on per-channel CAC may have higher true blended impact than the attribution shows; channels that look bad may be efficiently capturing demand created elsewhere.
Blended CAC is honest about the limits of attribution. It produces one number for the total cost of acquiring a customer, which finance and executives can reason about without needing methodology training.
How Blended CAC Works
Numerator: total marketing spend (paid, earned, owned-with-cost) for the period. Denominator: total new customers acquired in the period. Divide. Track over time; compare to LTV; benchmark against category.
The period matching matters. Marketing spend has carryover effects, so the customers acquired this month are partly from this month's spend and partly from previous months' spend. Most teams use trailing periods (rolling 90 days) to smooth this, or model the spend-to-acquisition lag explicitly.
In Practice
Blended CAC is the operational sibling of MER. Track them together; investigate together when either moves materially. A rising blended CAC with stable MER means revenue per customer is rising fast enough to absorb higher acquisition cost; rising blended CAC with falling MER means efficiency is eroding and warrants intervention.
How Presenc AI Helps
Presenc AI provides the AI visibility data that explains blended CAC trends when they cannot be explained by paid channel changes. A rising blended CAC with no obvious paid driver often reflects AI visibility erosion; a falling blended CAC with no obvious driver often reflects AI visibility gains. Presenc surfaces the AI side of the acquisition story that blended CAC alone does not break out.