Customer Acquisition Cost (CAC)

Customer Acquisition Cost (CAC) measures the total cost of acquiring one new customer. It is one of the most consequential KPIs in e-commerce, because paired with customer lifetime value it determines whether growth is profitable or merely expensive.

How to calculate CAC

CAC = total acquisition cost ÷ number of new customers

The denominator is the part most often got wrong. CAC counts only customers placing their first order. Dividing spend by all orders gives cost per order, not CAC, and because returning customers cost nothing to acquire, that figure will always look better than reality.

What belongs in the numerator

Restricting the calculation to ad spend understates CAC, sometimes substantially. A complete figure includes:

• Paid media spend across all acquisition channels
• Salaries for staff working on acquisition
• Agency and freelancer fees
• Copy, design and creative production costs
• Payment processing fees on first orders
• Tooling and platform costs attributable to acquisition

Whichever definition you adopt, apply it consistently. A CAC that changes because the cost basis changed, rather than because performance changed, is worse than no CAC at all.

Setting a maximum CAC

CAC is only interpretable against the value a customer returns. The two inputs that define your ceiling are the profitability of a customer's first order and their predicted customer lifetime value.

Comparing CAC to lifetime value shows whether you are acquiring customers worth having. A low CAC that attracts one-time discount buyers can be worse than a higher CAC that brings in customers who repeat. This is why CAC should be segmented — by channel, product category and market — rather than tracked only as a blended average, which hides both the best and worst performing sources.

When a high CAC is defensible

A temporarily elevated CAC can be rational: entering a new market, building brand awareness, or acquiring a cohort with strong retention characteristics. The distinction that matters is whether the elevated cost is a deliberate investment with a payback period you have modelled, or simply inefficiency that hasn't been noticed.

Related metrics

CAC sits alongside epROAS, which measures profit returned per unit of spend, and wasted ad spend, which identifies budget producing no profitable return. For measuring whether acquisition spend is genuinely incremental rather than capturing demand that already existed, see incrementality testing.