CAC Payback Period
How many months until a new customer pays back their acquisition cost — the cash-flow metric that keeps growth honest.
What is it?
CAC payback period is the number of months it takes a new customer's gross margin to repay what you spent acquiring them. Where LTV:CAC asks whether the economics work eventually, payback asks the sharper question: how long is your cash locked up in the meantime?
That makes it the growth-spend governor. Every dollar of CAC is paid today and recouped over the payback window — the longer the window, the more working capital growth consumes, and the more a downturn or churn spike hurts before you ever break even on a cohort.
How to calculate?
Divide CAC by the monthly gross margin a new customer generates: CAC ÷ (monthly revenue per customer × gross margin). A $2,000 CAC, recouped at $200 a month on a 75% margin — $150 of monthly margin — pays back in about 13 months.
Use gross margin, not revenue; the payback has to come out of what a customer actually contributes after cost of service. The stricter variant also nets out expected early churn, since some of the cohort never survives long enough to pay you back at all.
What is a good CAC payback?
Under 12 months is strong — each year's sales budget recycles itself annually. Twelve to 18 months is workable for SMB and mid-market SaaS; 18 to 24 is typical for enterprise, where bigger contracts justify the wait. Past 24 months, growth runs on financing rather than the product's own economics.
The tolerance scales with retention: an enterprise business with 120% NRR can afford a two-year payback because customers grow after breakeven, while an SMB product with 6% monthly churn may lose the median customer before month 17 ever arrives — a payback longer than the average lifespan means many customers never pay back at all.