CAC Payback Period

CAC payback period is the number of months it takes for a customer to repay what you spent acquiring them. You calculate it by dividing the cost to acquire a customer by the monthly gross profit that customer generates. If acquisition costs 600 EUR and each customer brings 100 EUR of gross profit a month, payback is six months.

For a lean, self-funded founder this metric is more useful than lifetime value, because it speaks directly to cashflow. A long payback period means you front the acquisition cost and wait, tying up cash you may not have. A short payback, ideally under twelve months for B2B subscriptions, means each customer refuels the tank quickly, letting you reinvest into acquiring the next one. It is the difference between growth that funds itself and growth that drains your account.

The trick is getting the two halves of the sum honest. Say you're running cold outreach with Instantly: tot up the seats, the email-warmup spend, and the hours you pour in, divide by the customers it actually closed, and that is your real CAC for the channel, not the rosy version. For the other half, the gross profit, pull each customer's true monthly margin from your books in Moneybird rather than guessing at revenue, because hosting and support costs quietly stretch the payback. Then watch the trend as you scale: say you're tracking signups and activation in Amplitude, and you notice newer cohorts paying back slower than older ones. That is the warning sign that you are reaching pricier, lower-fit customers, and it is far cheaper to catch it there than on your bank statement.