CAC, LTV and payback: the metrics that matter.
CAC is how much it costs to win a customer. LTV is how much margin that customer leaves while buying from you. Payback is the time they take to return what they cost. Read together, the three say whether the company’s growth pays for itself or is being financed by cash.
Fabrício MartinsFounder of Martin Marketing & Design
In short
- CAC: investment in marketing and sales divided by the new customers in the period.
- LTV: the margin a customer generates during the whole time they buy.
- Payback: CAC divided by the customer’s monthly margin.
- How to read them: LTV well above CAC and a payback your cash can handle.
Why these three and not others
Marketing produces numbers in abundance: reach, clicks, followers, leads. Almost all of them describe activity. Few say whether the company is making money from growth.
CAC, LTV and payback build that bridge between marketing and cash. They answer three questions every business owner should know by heart:
- How much do I pay to get a new customer?
- How much does that customer give back?
- In how long?
A company can double in size and go under, if each new customer costs more than they bring in or takes too long to return the investment. The three numbers show that before the cash does.
CAC: customer acquisition cost
CAC = investment in marketing and sales ÷ new customersBoth numbers need to be from the same period.
The calculation is simple. The difficulty is deciding what goes into the investment. For an honest number, add everything:
- Ad budget.
- Marketing and sales tools.
- Providers: agency, consultancy, content production.
- Salaries and commissions of those who work in marketing and sales.
A hypothetical example, for one month:
| Item | Amount |
|---|---|
| Ad budget | R$ 6,000 |
| Tools | R$ 500 |
| Management and creative | R$ 2,500 |
| Part of the sales salary | R$ 3,000 |
| Full | R$ 12,000 |
With 30 new customers in the month, the CAC is R$ 400. Anyone looking only at the ad budget would arrive at R$ 200 and make decisions with half of the real cost.
LTV: customer value over time
LTV stands for lifetime value. It is how much a customer generates while they keep buying. The most useful version uses margin, not revenue.
LTV = margin per purchase × purchases per year × years as a customer
In subscription businesses, the math is even more direct: monthly margin times the number of months the customer stays.
Following the example: a company charges R$ 200 a month and has a 60% margin. Each customer leaves R$ 120 in margin per month. If the average stay is 18 months, the LTV is R$ 2,160.
Use the margin. An LTV calculated on revenue looks much bigger than it is. The customer who pays R$ 3,600 over 18 months did not leave R$ 3,600 in the company.
When in doubt, prefer the conservative number. An optimistic LTV justifies spending your cash cannot handle.
LTV divided by CAC: how to read it
The number that sums up the two is the ratio between them. In the example, R$ 2,160 divided by R$ 400 gives 5.4. Every real invested to win a customer comes back 5.4 times in margin.
| LTV ÷ CAC | Reading | What to do |
|---|---|---|
| Below 1 | Every new customer means a loss | Stop scaling and fix the funnel |
| Between 1 and 3 | Growth pays for itself, barely | Improve retention or reduce the cost |
| Around 3 | The range considered healthy in the market | Grow with confidence |
| Well above 5 | High return per customer | Assess whether you can invest more and grow faster |
The range of 3 is a market reference, not a law. Businesses with low margins or tight cash need more room. And a very high ratio is not always good news: it can mean the company is investing too little and leaving market to the competitor.
Payback: how long until the cost comes back
The LTV to CAC ratio says whether the customer is worth it. Payback says when. And the when is what your cash feels.
Payback = CAC ÷ monthly margin per customer
In the example: R$ 400 divided by R$ 120 gives a little over three months. The company advances R$ 400 and only recovers it in the fourth month. Until then, every new customer is an investment not yet returned.
This explains why fast-growing companies can run out of cash. If 100 customers come in during the month, that is R$ 40,000 advanced. The longer the payback, the more capital growth demands.
- Short payback: growth finances itself.
- Long payback: you need a reserve or slower growth.
The same CAC in two businesses
CAC alone does not say whether acquisition is expensive or cheap. Compare two hypothetical businesses with the same cost of R$ 400 per customer:
| Subscription business | One-time purchase business | |
|---|---|---|
| Sale | R$ 200 per month | R$ 3,000, once |
| Margin | 60% | 30% |
| Time as a customer | 18 months | One purchase |
| LTV | R$ 2,160 | R$ 900 |
| LTV ÷ CAC | 5.4 | 2.25 |
| Payback | A little over 3 months | On the sale itself |
The first earns more per customer, but waits to receive it. The second recovers the cost right away, with a smaller return. Neither is better in absolute terms. They are different profiles, which call for different strategies: the first needs to take care of retention, the second needs referrals and a reason for the customer to come back.
Reading the three together: four situations
Each combination of the three numbers describes a different moment for the company and calls for a different decision:
| Situation | What it means | Decision |
|---|---|---|
| High LTV, low CAC, short payback | Growth pays for itself | Invest more, while the numbers hold |
| High LTV, high CAC, long payback | The customer is worth it, but takes time | Grow at the pace your cash can handle, or shorten the payback |
| Low LTV, low CAC | A cheap customer who brings in little | Work on retention and order value before scaling |
| Low LTV, high CAC | Every sale increases the loss | Stop investing in acquisition and review offer and audience |
The second row is the most dangerous, because it looks healthy. The ratio between LTV and CAC is good, the team celebrates and cash gets tighter every month. Companies in this situation need to look at payback before any growth goal.
How to improve each number
| Goal | Levers |
|---|---|
| Lower CAC | Increase website conversion, cut channels with no sales, invest in organic search and referrals |
| Increase LTV | Retain for longer, sell more often, raise the order value with bundles and add-ons |
| Shorten payback | Charge a deposit, offer a discounted annual plan, reduce the time between the lead and the sale |
An observation that changes priorities: increasing retention improves two numbers at once. The customer who stays longer raises LTV and, by referring others, lowers CAC. That is why so many growth teams start with it.
To locate where the loss happens, build the funnel stage by stage. The step-by-step guide is in how to build an AARRR funnel.
CAC and LTV by channel
Overall CAC is an average, and averages hide extremes. The next step is to calculate it by channel: how much each customer cost who came from ads, from organic search, from referrals.
Two surprises almost always appear. The first is that channels have very different costs. The second is that each channel’s customers behave in different ways: they stay more or less time, they buy more or less.
A channel with a high CAC can be the company’s best, if it brings customers who stay twice as long. And a channel with a very low CAC can bring people who cancel in the second month. Only the combined reading, channel by channel, shows where to put the next real.
For this to work, the source of each customer needs to be recorded from the first contact. It is one field on the form and one column in the spreadsheet.
What if the customer buys only once
Renovations, real estate, parties, some professional services: there are businesses where repeat purchases are rare by nature. The three metrics still apply, with adaptations.
- LTV is the margin of one sale. Plus, when it exists, what comes from complementary services.
- Referrals go into the math. If one in four customers refers another who closes, each sale is worth, in practice, more than one.
- Payback is immediate. The risk is not in the time frame, but in paying more for the customer than the margin of the sale.
In these businesses, the CAC ceiling is stricter. The math for how much you can invest in media is in how much to invest in ads.
Most common calculation mistakes
- Counting only media. Leaving salaries and providers out lowers CAC on paper and misleads the decision.
- Using revenue in LTV. What pays for CAC is the margin.
- Mixing periods. In long-cycle sales, the customer who closes today was won with the investment of months ago.
- Projecting retention with no data. A one-year-old company does not know whether the customer stays for five.
- Looking only at the average. Without the breakdown by channel, the best and the worst stay hidden.
- Calculating once and forgetting. Media costs and customer behavior change all the time.
The minimum spreadsheet
You do not need a system to start. A spreadsheet with one row per month and these columns does the job:
- Total investment in marketing and sales.
- New customers.
- CAC, which is the first divided by the second.
- Average monthly margin per customer.
- Customers who left in the month.
- Estimated average stay.
- LTV and payback, calculated from the previous ones.
Fill in the last six months at once and, from then on, one row per month. Before long you can see whether CAC is rising, whether customers are staying longer and whether growth remains healthy.
Frequently asked questions
One that fits comfortably within your LTV and your cash. There is no good amount in absolute terms: R$ 400 is cheap for someone with an LTV of R$ 2,000 and expensive for someone with an LTV of R$ 500. CAC only makes sense read together with the other two numbers.
Start with what is certain: the margin of the first sale. For retention, use a conservative estimate and review it every quarter, as the real data comes in. It is better to underestimate and get a nice surprise than to plan on a number that does not hold.
Churn is the rate of customers who cancel or stop buying in a period. It defines how long customers stay: with churn of 5% a month, the customer stays twenty months on average. Lowering churn is the most direct way to increase LTV.
No. CPA, cost per acquisition, usually measures the cost of a conversion inside an ad platform, such as a lead or a purchase. CAC considers the whole investment in marketing and sales and only counts those who actually became customers.
CAC, every month. LTV and payback, every quarter, because they depend on behaviors that change more slowly. Also recalculate whenever you change price, channel or offer.
Conclusion
CAC, LTV and payback fit in a spreadsheet and change the quality of every marketing decision. They replace the question "how much did we spend?" with "how much does each customer cost, how much do they give back and when?".
Calculate honestly, break it down by channel and review often. If you want to do this reading with guidance, get to know Martin’s growth marketing consulting.
