What is CAC and LTV in simple terms?

CAC (customer acquisition cost) is the total you spend on sales and marketing to win one new customer. LTV (lifetime value) is the total profit a customer brings over the whole time they stay with you. CAC is the cost to get a customer in the door; LTV is what they are worth once inside. A healthy business has LTV comfortably bigger than CAC.

How do you calculate CAC and LTV?

CAC is your total sales and marketing spend for a period divided by the new customers won in that period: 10,000 dollars over 50 customers is a 200 dollar CAC. A simple LTV formula is average monthly revenue times gross margin times average lifetime, where lifetime equals 1 divided by monthly churn. At 50 dollars a month, 80 percent margin, and 5 percent churn (20 months), LTV is 50 x 0.80 x 20 = 800 dollars.

What is a good LTV:CAC ratio?

The widely cited healthy benchmark is around 3:1, meaning each customer is worth about three times what you spent to acquire them. Below 1:1 you lose money on every customer and should not scale. A ratio much higher than 3:1, like 5:1 or more, can signal you are under-investing in growth and could spend more to grow faster. Pair it with a CAC payback period under a year.

Why does churn have such a big effect on LTV?

Because average customer lifetime equals 1 divided by your monthly churn rate, and LTV is directly proportional to lifetime. Cutting churn from 5 percent to 2.5 percent doubles the average lifetime from 20 months to 40 months, which doubles LTV with no change to pricing or acquisition cost. That makes reducing churn one of the cheapest and most powerful ways to improve your unit economics.

What is the most common mistake when calculating CAC?

Counting only ad spend and leaving out the salaries, tools, and overhead of the people doing sales and marketing. This makes CAC look artificially low and gives false confidence to scale. The honest, fully loaded CAC includes every cost of acquisition. Likewise, base LTV on gross profit rather than revenue and use realistic churn, or both numbers will flatter you toward bad decisions.

What Is CAC and LTV? The Math Behind Profitable Growth

What is CAC and LTV in plain English? A founder's guide to customer acquisition cost and lifetime value: clear definitions, the exact math with a worked example, the all-important LTV:CAC ratio, and the mistakes to avoid.

CAC is your customer acquisition cost: the total amount you spend on sales and marketing to win one new customer. LTV is the lifetime value of a customer: the total profit that customer brings you over the entire time they stay with you. Put simply, CAC is what it costs to get a customer in the door and LTV is what that customer is worth once they are inside. The whole game of building a profitable business is making sure each customer is worth more than you paid to acquire them. In this guide I will define both numbers clearly, walk through the exact math with a worked example, explain the LTV:CAC ratio that ties them together, and flag the mistakes that make these numbers lie.

What is CAC and LTV, really?

Every business that pays to grow faces the same fundamental question: am I making money on each customer, or quietly losing it? CAC and LTV are the two numbers that answer it. If you spend more to win a customer than that customer ever pays back, you have a machine that destroys money faster the more you feed it, no matter how impressive your growth chart looks.

CAC, customer acquisition cost, is the fully loaded cost of acquiring a new customer. That means everything you spend to get them: ad spend, the salaries of your sales and marketing people, the software they use, agency fees, and so on. You take all of that for a period and divide it by the number of new customers you won in that period. The honest version includes salaries and overhead, not just ad spend, because a customer who took an expensive salesperson five calls to close cost you far more than the ad click suggests.

LTV, lifetime value, is the total profit a customer generates over their entire relationship with you. It depends on three things: how much they pay you per month, how long they stay, and your profit margin on that revenue. A customer paying 50 dollars a month who stays two years is worth a lot more than one paying the same who leaves after two months. This is why churn rate sits right at the heart of LTV: the longer customers stay, the more each one is worth.

The exact math, with a worked example

Let me make both numbers concrete with simple figures. First, CAC. Suppose last month you spent 5,000 dollars on ads and 5,000 dollars on the salary and tools of the person running acquisition, and you won 50 new customers.

CAC = total sales and marketing spend / new customers acquired = 10,000 / 50 = 200 dollars per customer.

Now LTV. The simplest reliable formula uses three inputs: average monthly revenue per customer, your gross margin, and the average lifetime of a customer in months. Lifetime is just 1 divided by your monthly churn rate, so a 5 percent monthly churn means an average customer stays 1 / 0.05 = 20 months. Suppose each customer pays 50 dollars a month at an 80 percent gross margin.

Input	Value
Average revenue per customer	$50 / month
Gross margin	80%
Monthly churn rate	5%
Average lifetime (1 / churn)	20 months
LTV = 50 x 0.80 x 20	$800

So this customer is worth 800 dollars in lifetime profit and cost 200 dollars to acquire. That is a healthy picture: you make back four dollars for every one you spend to grow. Notice how sensitive LTV is to churn. If you cut monthly churn from 5 percent to 2.5 percent, average lifetime doubles to 40 months and LTV jumps to 1,600 dollars, with no change to your pricing or ad spend at all. Reducing churn is one of the most powerful ways to increase LTV.

The LTV:CAC ratio

Neither number means much alone; their relationship is what tells you whether your growth is healthy. The LTV:CAC ratio divides one by the other and is one of the most-watched numbers in all of SaaS.

LTV:CAC ratio = LTV / CAC. In our example that is 800 / 200 = 4, usually written as 4:1.

LTV:CAC ratio	What it usually means
Below 1:1	You lose money on every customer. Unsustainable; fix this before scaling.
Around 1:1 to 2:1	Barely profitable after overhead. Growth is fragile.
Around 3:1	The widely cited healthy benchmark for SaaS.
Much higher, like 5:1+	Very profitable per customer, but often a sign you are under-investing in growth and could spend more to grow faster.

The classic target is around 3:1. Below it, your unit economics are too thin to scale safely. Surprisingly far above it can also be a warning, not that you are doing badly, but that you are leaving growth on the table by being too cautious with your marketing budget. There is one more number people pair with this: CAC payback period, the number of months of revenue it takes to earn back the CAC. In our example, at 50 dollars a month and 80 percent margin you earn 40 dollars of gross profit per month, so a 200 dollar CAC pays back in 5 months. Shorter is better, because you get your cash back sooner to reinvest.

Common mistakes that make these numbers lie

CAC and LTV are easy to calculate badly, and a flattering miscalculation is worse than no number at all because it gives false confidence. Here are the traps I see most.

Leaving salaries out of CAC. Counting only ad spend makes CAC look artificially low. Include the salaries, tools, and overhead of everyone working on acquisition.
Using revenue instead of profit in LTV. LTV should be based on gross profit, not revenue. If your margin is 80 percent, a customer's revenue overstates their real value by 25 percent.
Ignoring churn in LTV. LTV is meaningless without a realistic lifetime, and lifetime comes straight from churn. Optimistic churn assumptions inflate LTV dramatically.
Mixing time periods. Make sure CAC and the spend behind it cover the same period as the customers you are counting, or you will divide this month's spend by last quarter's customers.
Forgetting payback. A great LTV:CAC ratio can still strangle you if the payback period is too long, because you run out of cash waiting to be repaid. Watch both.

The honest rule: be conservative. Use real, fully loaded costs in CAC, use gross profit and realistic churn in LTV, and your ratio will guide good decisions instead of cheering you toward a cliff.

Why these numbers decide your growth strategy

Once you trust your CAC and LTV, they stop being report-card figures and start driving decisions. A strong, well-understood ratio with a short payback period is what lets you pour money into growth with confidence, because you know each dollar of marketing comes back multiplied. A weak ratio is a signal to stop scaling and fix the underlying business first, usually by lowering CAC, raising prices, improving margins, or cutting churn.

This is also why these numbers matter so much before you ever spend heavily on growth. Pouring marketing money into a product with bad unit economics just helps you lose money faster, which is the same trap I describe in my guide on product-market fit: scaling before the fundamentals are sound burns runway. And if you are still at the stage of weighing whether an idea is worth building at all, understanding the lifetime value side helps you judge whether the eventual customers could ever justify the cost to build the product in the first place.

The bottom line

CAC is what you spend to win a customer, and LTV is the lifetime profit that customer brings. The business works when LTV comfortably exceeds CAC, with the widely used benchmark being an LTV:CAC ratio around 3:1 and a payback period of under a year. LTV is enormously sensitive to churn, so keeping customers is often the cheapest way to improve your economics. Calculate both conservatively, with fully loaded costs and gross profit, and the ratio becomes a reliable compass: green light to scale when it is strong, red light to fix the fundamentals when it is not.

If you want help working out your real CAC and LTV, building the dashboards to track them, or deciding whether your unit economics are ready to scale, that is exactly the kind of analysis I do with founders. Book a call and bring your numbers, or reach out through the contact form, and I will help you see whether your growth is actually profitable.