Customer Acquisition Cost (CAC) – This is the total acquisition cost for a customer. If you are calculating your ROAS here, all marketing channels that have been part of the customer journey should be summed up. It is also important to decide whether it is ROAS or ROI you want to calculate – whether costs other than direct marketing costs should be included. Together with LTV , CAC is one of the two most central KPIs for subscription services (SAAS).