Cost Per Acquisition (CPA)
The cost of acquiring one customer through a specific channel or campaign — a narrower, channel-level cousin of CAC.
CPA and CAC are not the same
CPA is usually channel-scoped and counts programme spend. CAC is company-wide and fully loaded, including salaries. Presenting CPA as CAC understates acquisition cost substantially.
It inherits attribution's limits
How to compute it without misleading anyone
Scope it to a channel or campaign and say so in the label. An unscoped CPA reads as CAC and is materially smaller.
Count programme spend for the period that produced the customers, not the period they closed in. With any sales cycle these differ.
Decide whether people costs are included. CPA conventionally counts programme spend only, which is exactly why it is not comparable to CAC.
State the attribution model in the same breath. CPA is a cost divided by an attributed count, and changing the model changes the number without any spend changing.
Compare channels on CPA and on downstream retention together. The cheapest channel to acquire from is frequently not the cheapest to keep.
Where it misleads
Presenting CPA where the audience expects CAC understates acquisition cost substantially, and it is a common and rarely deliberate error.
It inherits every weakness of the attribution model underneath it, and those weaknesses are invisible in a single figure.
Channel-level CPA ignores interaction between channels, so it credits the last measurable step in a sequence that needed all of them.
Optimising to the lowest CPA drives spend towards the most measurable channels rather than the most effective ones.
RELATED TERMS
Cost Per Lead (CPL)
Marketing spend divided by leads generated. The most immediately available demand-gen metric and the easiest to misread.
Magic Number
A sales efficiency measure comparing new recurring revenue produced to the sales and marketing spend that produced it.
Customer Acquisition Cost (CAC)
The fully loaded cost of acquiring one new customer: sales and marketing spend for a period divided by new customers acquired from it.
Attribution
The methodology connecting marketing touchpoints to revenue outcomes, so investment can be allocated on evidence rather than on preference.
Attribution Model
The specific rule assigning credit for a conversion across the touchpoints that preceded it.
COMMON QUESTIONS
- What is cost per acquisition?
- The cost of acquiring one customer through a specific channel or campaign, calculated as programme spend divided by customers attributed to it. It is channel-scoped and counts media and programme cost, which makes it a narrower measure than fully loaded customer acquisition cost.
- What is the difference between CPA and CAC?
- Scope and inclusion. CPA is usually channel-level and counts programme spend only. CAC is company-wide and fully loaded, including sales and marketing salaries and tooling. CAC is therefore substantially larger, and presenting CPA where someone expects CAC understates acquisition cost — a common and rarely deliberate error.
- What is a good CPA?
- There is no transferable figure, because CPA depends entirely on price point, margin and which channel is being measured. The meaningful test is CPA against the gross profit the customer produces and against how long they stay — a low CPA on customers who churn in four months is worse than a higher one on customers who do not.
- Why does our CPA differ between reports?
- Almost always the attribution model or the time window. CPA is a cost divided by an attributed customer count, so switching from last-touch to first-touch, or changing the lookback period, moves the number without any spend changing at all. State the model alongside the figure or the figure is not comparable to itself.
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