Customer acquisition cost (CAC) is the total sales and marketing investment required to win one new customer, divided by the number of customers won in a period. A fully loaded CAC includes salaries, commissions, ad spend, tooling, and overhead, not just media budget, so it reflects the real cost of growth.
CAC only means something in relation to what a customer returns. That is why it is almost always read next to lifetime value as the LTV:CAC ratio, and why CAC payback period, the number of months of gross profit it takes to earn the acquisition cost back, is one of the most scrutinized efficiency metrics in SaaS.
Why retention is a CAC strategy
The cheapest customer is the one you already have. Retaining an account carries effectively zero new acquisition cost, and expansion revenue from the existing base improves blended CAC efficiency without spending a dollar more on acquisition. A customer success team that prevents churn is, in financial terms, lowering the company effective cost of growth.
- High churn forces you to acquire more just to stand still, which inflates effective CAC.
- Strong net revenue retention means existing customers fund growth, reducing dependence on paid acquisition.
- Catching every at-risk account protects the acquisition investment already sunk into that customer.