What Is the CAC Payback Period?
The CAC payback period is the number of months a business needs to recover the cost of acquiring a new customer, using the gross margin that customer generates each month. It is one of the most important unit-economics metrics for SaaS and subscription businesses because it tells you how long your cash is tied up before a customer becomes profitable. A shorter payback period means faster capital recycling and a healthier, more scalable growth engine.
How to Use This Calculator
Enter three numbers: your Customer Acquisition Cost (CAC) — the total sales and marketing spend divided by new customers won; the monthly revenue per customer (ARPU); and your gross margin percentage. The calculator multiplies ARPU by the gross margin to get the monthly gross margin per customer, then divides CAC by that figure to return the payback period in months.
The Formula Explained
$$\text{Payback (months)} = \frac{\text{CAC}}{\text{ARPU} \times \dfrac{\text{Gross Margin (\%)}}{100}}$$ Using gross margin rather than raw revenue is essential — you only recoup CAC from the profit a customer leaves behind after the cost of serving them, not from top-line revenue.
Worked Example
Suppose CAC is $1,200, ARPU is $100/month, and gross margin is 80%. Monthly gross margin per customer = \(100 \times 0.80 = \$80\). $$\text{Payback} = \frac{1{,}200}{80} = 15 \text{ months}$$ The business recovers its acquisition spend after about 15 months of that customer's subscription.
FAQ
What is a good CAC payback period? For SaaS, under 12 months is excellent, 12–18 months is healthy, and over 24 months may signal inefficient acquisition or pricing.
Why use gross margin instead of revenue? Because servicing costs (hosting, support, payment fees) reduce what's actually available to repay CAC. Revenue alone overstates how quickly you break even.
Does this include churn? No — this is the simple payback formula. If churn is high, customers may leave before payback completes, so compare payback against your average customer lifetime.
