Cost per action (CPA) is an online marketing measurement of any action you perform for your business to increase customer acquisition. Some of the examples are a click, sign up, and so on. You can calculate the CPA by dividing the total spend by the total number of conversions.
CPA = Total spend / Total number of conversions
CPA indicates the cost of an action using marketing, and you can use it as one of the factors to determine the spend for specific marketing objectives.
Incremental CPA (ICPA)
The incremental CPA is the cost per incremental conversion. An incremental conversion is a paid conversion. You can use this measurement to identify the cost to acquire a customer using paid media channels. However, you can obtain this value only for the past data.
Marginal CPA (MCPA)
The marginal CPA (MCPA) shows the price for your next conversion, considering your current and historic spend. It is the change in the CPA for the next incremental conversion compared to the current CPA and indicates the saturation of a source. Hence, based on this metric, you can identify the least expensive source for your next conversion.