# CPA in marketing: formula and how it differs from CAC

> Name the action and included costs before comparing CPA with the cost of acquiring a new customer.


**In marketing, CPA is cost per action: included marketing costs ÷ completed actions you define.** A signup, enquiry, and purchase are different events. State which one you count before interpreting the figure.

## What counts as an action

CPA often means *cost per action*, though some contexts use it for *cost per acquisition*. The acronym alone does not identify the outcome. Write “CPA per signup,” “CPA per enquiry,” or “CPA per purchase” to make the denominator clear.

Google Ads defines an action as an outcome a campaign seeks, such as a purchase, registration, or signup. Its formula divides marketing cost by the number of actions. This is that platform’s definition; each report still needs to state which cost and event it records. [Read Google Ads’ cost per action definition](https://support.google.com/google-ads/answer/13278730?hl=en).

Do not change “marketing cost” to “ad spend only” without checking the data’s scope. State which costs you include, which campaign or channel they cover, and the period.

## What changes when you calculate CAC

Customer acquisition cost divides the included sales and marketing costs by the number of new customers in the same period. Stripe describes this calculation for SaaS businesses and notes that sales cycles can delay conversions, so costs and customers need to be read together over time. It is a contextual method for SaaS, not a standard for every business. [Read Stripe’s SaaS CAC guide](https://stripe.com/resources/more/cac-in-saas).

| Measure | Calculation base | What it answers |
| --- | --- | --- |
| CPA per action | Included marketing costs ÷ number of defined actions | What did each signup, enquiry, or purchase cost? |
| CAC | Included sales and marketing costs ÷ new customers | What did it cost to bring in each new customer? |

The CPA base may be the cost of a campaign or a broader marketing cost, depending on the report and the decision you need to make. For CAC, state which sales and marketing costs you count and when someone becomes a new customer.

## Compare two denominators

Consider two fictional calculations for the same period:

- A campaign records 40 enquiries, and the team includes 1,200 currency units in marketing costs for those actions. Its CPA per enquiry is 1,200 ÷ 40 = **30 per enquiry**.
- The business records 10 new customers and includes 6,000 currency units in sales and marketing costs for that calculation. Its CAC is 6,000 ÷ 10 = **600 per new customer**.

The figures answer different questions. The example is not a budget recommendation or a result from a real business. A CPA per purchase can equal CAC if it counts new customers and uses the same costs, period, attribution, and acquisition rule. If it counts enquiries or signups, its denominator is not customers.

With zero actions, this formula does not produce a CPA; do not report it as zero. The same applies to CAC when there are no new customers.

## State these details before comparing figures

Record these items next to each number:

- **Event:** signup, lead, purchase, or another specific action.
- **Included costs:** media spend, marketing costs, or other defined sales and marketing costs.
- **Period and attribution:** when costs accrue and when an action or customer is counted.
- **New-customer rule:** what date or status marks acquisition and how duplicates are removed.

Then compare metrics with matching scope. If your team uses CPA per lead, read it alongside [cost per lead (CPL)](/en/guides/cost-per-lead/), but do not treat it as cost per customer. The next question depends on which stage you need to understand: recorded actions, valid leads, or new customers.

The cover illustration was generated with AI.

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