Customer acquisition cost and how many months a customer takes to pay it back.
CAC payback period = customer acquisition cost ÷ monthly gross profit per customer. CAC is everything you spent on sales and marketing in a period (ads, tools, freelancers) divided by the new customers it brought in.
Use gross profit, not revenue: a $29 plan with $6 of hosting, AI and payment costs only pays back $23 a month.
LTV is a forecast; payback is cash. If a customer takes 18 months to repay what you spent to win them, every new customer makes you poorer for a year and a half. Bootstrapped founders usually aim for under 12 months, and under 6 when growth is paid from revenue.
When you're doing things that don't scale - personal outreach, communities, posting - your real CAC is your time. Track the hours too.
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