CAC payback tells you whether your growth is affordable. It asks how many months of gross profit from a new customer it takes to earn back what you spent to win them. Until that point, every new customer has cost you money.
Worked example
Start with customer acquisition cost (CAC): what you spent on sales and marketing to win new customers in a period, divided by the number of new customers won.
| Step | Calculation | Result |
|---|---|---|
| New-business sales and marketing cost (quarter) | salaries, commissions, programs, tools | $900,000 |
| New customers won (quarter) | 30 | |
| CAC | $900,000 ÷ 30 | $30,000 |
| Gross profit per customer per month | $1,500 new MRR × 80% gross margin | $1,200 |
| CAC payback | $30,000 ÷ $1,200 | 25 months |
Each new customer has to stay for more than two years before it has paid back the cost of winning it.
Why gross margin belongs in the formula
Revenue isn't profit. Hosting, support and other costs of delivering the service come out of every dollar a customer pays, and only what's left can repay acquisition cost. Leave margin out and the same company appears to pay back in $30,000 ÷ $1,500 = 20 months: five months shorter than reality.
Reading the result
CAC payback has three levers: lower CAC, higher new MRR per customer, or higher gross margin. In the example, cutting CAC from $30,000 to $24,000 would bring payback down to $24,000 ÷ $1,200 = 20 months.
As an illustrative rule of thumb, many subscription businesses aim for payback under 24 months. It is a rule of thumb, not a benchmark: the right answer depends on how long your customers stay, how much they expand, and how much cash you have. A 25-month payback is fine if customers stay ten years and alarming if half of them leave in year two. That's why payback should always be read alongside retention, especially gross revenue retention, and expansion, which net revenue retention captures. Watch your own trend over time.
Agree what goes into CAC
Payback is only comparable over time if the cost definition stays fixed. Agree with finance, in writing:
- Which salaries count (sales, marketing, sales development, managers, sales engineers?).
- Whether commissions, tools, events, agency and partner fees are in.
- That only new-business cost counts. Account management and customer success costs for existing customers belong elsewhere.
- Which period's spend is matched with which period's customers. With long sales cycles, some teams lag spend by a quarter; whatever you choose, keep it consistent.
Common mistakes
- Using revenue instead of gross profit. Payback looks shorter than it is.
- Leaving costs out of CAC. Excluding salaries or tools flatters the number and makes it incomparable with last year's.
- Mixing new and existing customers. Expansion revenue from existing customers is not new MRR from the customers that CAC paid for.
- Using bookings instead of recurring revenue. A multi-year contract booked in full is not monthly recurring revenue.
- Reading payback without retention. A customer who churns before payback is a net loss, whatever the average says.
The free RevOps Foundations course covers CAC payback in Lesson 3, "The metrics that matter".