Hong Life CalculatorsUnderstanding the CAC payback period calculator — concept and principle
The CAC payback period is the number of months it takes for a new customer's gross profit to repay the cost of acquiring them. Subscription businesses, SaaS companies and their investors use it because it links growth to cash: the longer the payback, the more money a company must invest up front before new customers start paying for themselves.
How it is calculated
- Monthly gross profit per customer = monthly revenue per customer × gross margin.
- Payback period (months) = CAC ÷ monthly gross profit per customer.
CAC is the fully loaded cost to win one customer (sales plus marketing). Monthly revenue per customer is often called ARPA or ARPU. Gross margin is a percentage. The calculator works with any currency.
The principle
A new customer starts as a cost and slowly pays it back each month. Revenue alone does not repay CAC, because part of each payment covers the cost of delivering the service, such as hosting, support and payment fees. Only gross profit is available to recover acquisition spend. Dividing CAC by that monthly amount tells you how many months it takes. The formula assumes the customer stays at least that long and that revenue and margin are constant.
Worked example
- Inputs: CAC $600, monthly revenue per customer $80, gross margin 75%.
- Monthly gross profit = $80 × 0.75 = $60.00.
- Payback period = $600 ÷ $60 = 10 months.
How to read the result
Shorter is better. Paybacks under about 12 months are widely regarded as strong for SaaS businesses selling to small and mid-sized customers; enterprise software often accepts longer periods because contracts are larger and customers stay longer. Compare payback with average customer lifetime: if customers typically cancel after 8 months, a 10-month payback means most of them never repay their acquisition cost. You can shorten payback by lowering CAC, raising prices, improving gross margin or collecting annual payments up front.
Common mistakes
- Dividing CAC by revenue instead of gross profit, which makes payback look shorter.
- Using marketing-only CAC and leaving out sales costs.
- Ignoring churn, so some customers leave before payback.
- Mixing yearly and monthly figures.
Frequently asked questions
What is a good CAC payback period?
It depends on the market. Under 12 months is often cited as strong for SaaS; what matters most is that payback is well within the typical customer lifetime.
Should I use revenue or gross profit?
Gross profit. The part of revenue that pays for delivering the service is not available to repay acquisition costs.
How does churn change payback?
Churn means some customers leave before they have repaid CAC, so the average cohort takes longer to pay back than the simple formula shows.
Sources: David Skok, "SaaS Metrics 2.0 – A Guide to Measuring and Improving What Matters" (forentrepreneurs.com)