Blended CAC: how to calculate customer acquisition cost across all channels

Blended CAC is total sales and marketing spend divided by the number of new customers in the same period. It counts every new customer, paid or organic, so strong organic growth pulls it down.

The blended CAC formula

Blended CAC is commonly defined as:

Blended CAC = total sales and marketing spend ÷ new customers in the same period

Metabase's metrics guide puts it the same way: "Blended CAC divides all acquisition spend by all new customers, organic included." (Metabase)

Blended CAC vs paid CAC

Paid CAC uses paid media spend only, divided by the new customers your attribution gives to paid channels. It tells you whether the ads themselves are working, but it depends on how those customers were attributed.

Blended CAC uses everything, divided by every new customer. It needs no attribution at all, which makes it easy to check. The cost is that it can't tell you which channel is doing the work, and good organic months make it look better than paid is doing.

Keep them on separate lines in a report. Don't swap one for the other.

Illustrative example

Round numbers, not a customer. In one month:

Ad spend: €15,000

Other sales and marketing costs (tools, content, agency fee): €5,000

New customers: 400, of which your attribution gives 250 to paid ads

Blended CAC = €20,000 ÷ 400 = €50

Paid CAC = €15,000 ÷ 250 = €60

Same month, two honest numbers. Blended is lower because the 150 customers who didn't come from ads still count.

Why "new customer" needs payment data

The bottom of the fraction is the hard part. A sign-up isn't a customer. A returning buyer isn't new.

A rule that holds up: a new customer is someone whose first successful payment falls in the period. Your payment processor already knows this, because it has every payment by customer. Pull first payments for the month, after refunds, and count them. Lead counts and platform conversions both include people who never paid.

Pairing it with MER

Blended CAC and MER belong together. MER tells you how much revenue the spend brought in overall. Blended CAC tells you what each new customer cost. One r/PPC reply put the risk of MER on its own like this: "Blended MER can look healthy while you're quietly getting more efficient at harvesting existing customers" (r/PPC, August 2026).

For the wider picture on blended numbers vs platform numbers, see blended ROAS and MER vs platform ROAS. To see how far platform-reported revenue sits from your payments, try the platform vs payment gap calculator.