CPO / CAC in practice.
These metrics are more meaningful than the cost per click, because they can be measured directly against your margin: if a sale earns you £12 of contribution margin, your CPO can sit below that. For products that get repurchased, it's worth looking at customer value over the whole relationship – then the CAC on the first purchase can be higher too.
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The difference and why it matters.
CPO measures advertising cost per order – regardless of whether it was a new or existing customer. CAC refers exclusively to newly won customers and is therefore the tougher metric.
For businesses with repeat purchases the difference is decisive: if a customer buys four times on average, acquiring new customers can cost considerably more than a single order is worth. This calculation is called the ratio of customer lifetime value (CLV) to CAC.
As a rough guide, a CLV-to-CAC ratio of around 3:1 is considered healthy. Below that, you're buying growth too expensively; well above it, you're leaving growth on the table.
Reducing CPO and CAC.
Email flows and subscription models reduce CAC over time, without more advertising budget.
More purchases from the same traffic reduce both metrics directly.
Not every channel delivers the same customer quality – some bring cheap clicks and expensive customers.
A higher basket value justifies a higher CPO.
Analyse retargeting campaigns separately, otherwise they flatter your CAC.
Common mistakes.
Looking only at the first purchase. If you ignore customer value over time, you massively underestimate the budget you could spend on advertising.
Mixing new and existing customers together. The resulting average leads to the wrong decisions.
Staring at the cost per click. One expensive click with a high conversion beats ten cheap ones with no purchase.
Frequently asked questions about CPO / CAC.
How do I calculate CAC?
What is a good CAC?
Does this apply on Amazon too?
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