Metric 05
CAC and LTV
Customer acquisition cost is everything you spent to get a customer, divided by the customers you got. Everything means media, lead purchases, agency fees, and the loaded cost of the people doing the selling. Lifetime value is gross profit per customer per period multiplied by how many periods they stay. Use gross profit, not revenue. Revenue-based LTV is the single most common way a business talks itself into an unprofitable channel. The ratio between them is the number that matters, and we have written the long version of that argument.
CAC = (media + lead purchases + agency fees + loaded sales payroll) ÷ new customers, same window.
LTV = average gross profit per customer per period × average number of periods retained.
Reported as LTV : CAC, with the retention assumption stated.
Those five definitions are the five systems a diagnosis grades. If you want a rough read on which one is leaking before you go pull the real numbers, the ten-question revenue leak quiz scores them in about two minutes.