Cost per Acquisition (CPA)

Technical explanation

CPA = included campaign or channel cost ÷ counted acquisitions. An acquisition must be defined explicitly—for example, a purchase, subscription, qualified opportunity, or another conversion—and matched to the same scope, period, attribution rules, and currency as the numerator. Advertising platforms often use CPA to mean cost per action or conversion, which may not represent a new customer.

Business relevance

CPA helps teams compare the efficiency of campaigns and bidding strategies against the economic value of the acquired outcome. Used with conversion value, margin, retention, and lifetime value, it informs budget and optimisation decisions.

Implementation example

A campaign spends £12,000 and records 160 attributed new subscriptions under a documented attribution window, producing a CPA of £75. The team separately monitors cancellations and gross margin before deciding whether the campaign is economical.

Limitations and common misconceptions

CPA changes with attribution, conversion definitions, delayed outcomes, refunds, duplicate conversions, and which costs are included. It is not necessarily customer acquisition cost, does not prove incrementality, and can look efficient while acquiring low-value or unprofitable customers.

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