Blended CAC: what it is and when to use it

When platforms disagree about who deserves credit, blended CAC answers a plainer question: what did a new customer cost us in total?

The formula

Blended CAC = total marketing spend / new customers in the same period. It includes every channel, so no platform gets to decide the denominator.

Count only new customers

Repeat purchases do not belong in the denominator. Take new customers from the store's own order data, with a first-order flag, rather than from any ad platform.

Example with made-up numbers: spend of 20,000 and 500 first-time customers gives a blended CAC of 40.

What to compare it with

Contribution per first order: if blended CAC is above it, the first order loses money.
Customer lifetime value, stated as an estimate with its assumptions.
Last month and the same month last year, with the same spend definition.

What to include in spend

Decide once whether agency fees, creative production and tools count, and write it down. Changing the definition between months makes the trend meaningless.

You can calculate it in the MER and blended CAC calculator.

5 min read. Last updated 2026-10-07. Examples use made-up numbers.

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Contribution per first order: if blended CAC is above it, the first order loses money.
Customer lifetime value, stated as an estimate with its assumptions.
Last month and the same month last year, with the same spend definition.