What CAC payback actually measures
CAC payback is the number of months of gross profit — not revenue — needed to recover what you spent acquiring a customer. The gross profit distinction matters: a company with 80% margins and one with 40% margins can report the same CAC and have wildly different economics.
The formula is straightforward:
- CAC = total sales and marketing spend ÷ new customers acquired
- Monthly gross profit = average revenue per account × gross margin
- Payback = CAC ÷ monthly gross profit
Include everything in the spend figure. Ad budget, marketing salaries, sales commissions, agency retainers, and the tools that support them. Excluding salaries is the most common way founders accidentally report a payback period half its real length.
Why the benchmark is 12 months
At seed and Series A the expectation is recovery inside 6–12 months. Beyond 18 months you are financing each customer for over a year before they contribute anything, which means growth consumes cash at a rate that outpaces most early-stage runways. Investors treat a long payback as evidence that the acquisition motion has not been proven, regardless of how fast top-line revenue is growing.
Questions
Should I use revenue or gross profit?
Gross profit. Using revenue overstates how quickly you recover the cost, sometimes by a factor of two. If your gross margin is 70%, only 70 cents of every revenue dollar is available to pay back acquisition cost.
Do I include salaries in CAC?
Yes. Fully loaded sales and marketing salaries, commissions, contractors and tooling all belong in the numerator. Excluding them is the single most common reason a reported payback period is wrong.
What if my payback is under 6 months?
That usually means you are under-investing in acquisition rather than that you are exceptionally efficient. If payback is very short and growth is slow, you can likely afford to spend more.
How does this relate to LTV:CAC?
Payback measures speed of recovery; LTV:CAC measures total return. A company can have a healthy 3:1 ratio and still run out of cash if payback takes 30 months.