Subscriber Acquisition Cost (SAC) is similar to CAC but specifically focused on the subscription context. It includes all costs associated with converting a prospect into an active paying subscriber, including free trial support costs.

Example: A consumer SaaS app spends $50 on average in paid ads and onboarding support to convert a free user into a paying subscriber at $15/month. With a 24-month average subscription length, the lifetime value is $360, giving a healthy SAC-to-LTV ratio of 1:7.2.