How many months of one customer's gross margin it takes to earn back what winning them cost. A date, where the LTV:CAC ratio is a forecast.
In practice
The LTV:CAC ratio is the most-quoted acquisition metric; CAC payback is the one that actually binds a company without three years of cash in the bank. The difference comes down to one word: LTV:CAC is a forecast, built on a churn rate projected years out — the least reliable number a young company owns — while payback is a date, computed only from figures you already have. Both come from the same three inputs and can flatly contradict each other: excellent unit economics over five years say nothing about your ability to fund next month. When they disagree, the date is the one your bank account respects.
The formula
CAC payback (months) = CAC ÷ (monthly revenue per customer × gross margin)
- CAC
The fully loaded cost of winning one customer — ads, tools, agencies, content and the salaries of the people selling and marketing. Leaving the salaries out is the most common mistake.
- Gross margin
What is left of the customer's payment after the direct cost of serving them: hosting, payment fees, support, any usage-based cost. Typically 70-85% in SaaS, much lower in anything with human delivery.
- Monthly revenue per customer
What one customer pays per month. For annual contracts, use the monthly equivalent for the calculation and read the FAQ on prepayment, which changes the cash answer completely.
Using revenue instead of gross margin is the version that flatters you, and it is the version most often quoted in a board deck. Margin is what actually pays the CAC back; revenue has the hosting bill still to pay out of it.
Worked example
The same €500 customer, followed forward
- CAC of €500: €60,000 of quarterly spend for 120 new customers.
- The customer pays €50 a month at 80% gross margin, so €40 a month actually comes back. Payback = 500 ÷ 40 = 12.5 months.
- Computed on revenue instead of margin: 500 ÷ 50 = 10 months. Two and a half months of difference, entirely produced by which number you divide by.
- At 3% monthly churn the average customer stays about 33 months (1 ÷ 0.03). So after payback there are roughly 20 months of margin left: 20 × €40 = €820 of profit per customer, and an LTV:CAC of about 2.6:1 — under the 3:1 most investors quote.
Payback and LTV:CAC were computed from the same three numbers and say different things. Payback says when the cash comes back; LTV:CAC says whether it was worth it at all. A company short on cash is bound by the first long before the second.
Orders of magnitude
- The targets most commonly quoted: under 12 months for SaaS sold to small businesses, and 18-24 months in enterprise sales, where contracts are larger and longer and the money is usually collected up front. Both are rules of thumb from a decade of venture-funded SaaS, not laws.
- The comparison that decides whether a payback is survivable is with your runway, not with a benchmark. A 14-month payback is fine with three years of cash and fatal with nine months of it — the same number, two different companies.
- A payback longer than the average customer lifetime is not a slow business, it is a business that loses money on every sale. That check takes one division and is skipped surprisingly often.
How to improve it
- Bill annually, with a discount if needed. Collecting twelve months up front can take payback to the day of signature — the strongest lever on this number, and the only one that works without changing the product or the funnel.
- Work the margin before the price: a support cost or an infrastructure bill cut in half moves the denominator just as surely as a price rise, and nobody churns over it.
- Compute payback per channel, not blended. The blended number is an average over channels that often differ by a factor of five, and it hides both the channel to stop and the one to pour into.
- Shorten the sales cycle. Time between the spend and the first payment is dead money that the formula does not show, and a cycle cut from ten weeks to four is worth more than most pricing changes.
In the Tour
Do you know your customer acquisition cost, even roughly?
- Yes, a solid number20 pts
- A rough estimate7 pts
- No idea0 pts
The Tour asks whether you know your CAC at all, even roughly — worth 20 points, against 7 for an order of magnitude and 0 for no idea. Payback is the next question after that one, and it is why the Tour asks: a CAC on its own is a number, a CAC next to a monthly margin is a decision about whether to spend more next month. Teams that answer 0 here are usually not bad at arithmetic; they have simply never put the two figures side by side.
Questions people ask
CAC payback or LTV:CAC — which one should I watch?
Both, and they answer different questions. LTV:CAC is a forecast: it depends on a churn rate projected years out, which is the least reliable number a young company owns. Payback is a date, built from figures you already have. When the two disagree, the date is the one your bank account will respect.
Should I use gross margin or revenue?
Gross margin. Revenue has not yet paid for hosting, payment processing or support, so a payback computed on it claims money back that is already spent. Whichever you pick, write it down next to the number: most disagreements about payback turn out to be two people using two formulas.
What changes if customers prepay a year?
The cash payback can drop to zero — the money is in the bank before the CAC invoice clears — while the accounting payback is unchanged. Both are true and they are used for different decisions: cash payback for how fast you can reinvest, accounting payback for whether the unit economics work.
Does payback include the sales cycle?
The standard formula does not, which is fine for self-serve and misleading for anything with a long cycle. If three months pass between the spend and the first euro collected, add them: a 12-month payback that is really 15 is the kind of gap that only shows up as an unexplained cash shortfall.