Customer acquisition cost (CAC)

The fully loaded sales and marketing spend required to win one new customer, computed as that spend over a period divided by the new customers it produced.

Set against a customer's lifetime value, it tells you whether growth is profitable or bought at a loss, and a business hiding rising acquisition cost is hiding a broken engine.

In numbers: A shop spending $40k on ads and sales in a quarter to land 200 customers has a $200 customer acquisition cost.