CAC vs CPA
CAC and CPA both express cost per outcome. The difference is what counts as the outcome — and that's usually where teams talk past each other.
The key difference: CPA is cost per any defined action; CAC is cost per paying customer specifically.
| Dimension | CAC | CPA |
|---|---|---|
| Outcome counted | Paying customer | Any action — lead, signup, install |
| Costs included | All sales + marketing spend | Usually ad spend only |
| Scope | Whole funnel | A single campaign or channel |
| Reported to | CFO, board | Performance marketing team |
| Useful for | Unit economics, payback period | Channel optimisation |
When to use CAC
Use CAC when you're modelling the business — payback, LTV:CAC, profitability.
When to use CPA
Use CPA when you're tuning a campaign, a creative, or an audience inside a channel.
FAQs
Is CAC just CPA at the bottom of the funnel?
In a self-serve PLG business, basically yes. In sales-led B2B, CAC also includes AE salaries, SDR cost and onboarding — which CPA usually ignores.
Why is CAC almost always higher than CPA?
Because only a fraction of actions become paying customers, and CAC absorbs all funnel costs, not just ad spend.
Which one matters more?
CAC, because it lines up directly against LTV. CPA is a tactical input that helps you bring CAC down.