CAC, LTV and Payback Explained, With a Worked Example

What is customer acquisition cost (CAC)?

Customer acquisition cost is what it costs to win one new customer. The formula is total sales and marketing cost in a period divided by the number of new customers won in that period. Include everything you spend to acquire: ad spend, tools, agency fees, and the salaries of the people doing sales and marketing. Leaving salaries out is the most common way teams make CAC look better than it is.

Calculate it per channel as well as blended. A healthy blended CAC can hide one channel that costs three times as much as the others.

It also helps to separate new-customer CAC from the cost of winning back former customers, because the two behave differently and mixing them hides both.

What is customer lifetime value (LTV)?

Lifetime value is the profit you expect from a customer over the whole relationship. For a subscription business a simple version is: average monthly revenue per customer × gross margin ÷ monthly churn rate. Dividing by churn gives the expected lifetime in months; multiplying by margin turns revenue into profit.

Use gross margin, not revenue. A customer paying $100 a month at 80% margin is worth $80 a month to you, not $100. LTV built on revenue overstates value and leads to overspending on acquisition.

How do you work out LTV:CAC and payback?

Here is a worked example with illustrative numbers. A product charges $100 a month at 80% gross margin, and 3% of customers cancel each month. LTV = $100 × 0.80 ÷ 0.03 = $2,667. If the company spent $60,000 on sales and marketing last quarter and won 75 customers, CAC = $60,000 ÷ 75 = $800.

LTV:CAC = $2,667 ÷ $800 = 3.3. CAC payback = CAC ÷ monthly gross profit per customer = $800 ÷ $80 = 10 months. In plain terms, each customer pays back their acquisition cost in about ten months and is worth about three times what they cost to win.

What benchmarks should you compare against?

The most quoted guidance comes from David Skok's SaaS Metrics 2.0. He writes that the best SaaS businesses have an LTV to CAC ratio higher than 3, sometimes as high as 7 or 8, and that many of the best recover their CAC in 5–7 months, while recovery beyond 12 months leads to weak profitability.

Treat these as rules of thumb, not targets. A ratio far above 5 can mean you are under-investing in growth. A ratio below 3 with a long payback means each new customer ties up cash for a long time, which matters more when money is expensive.

What mistakes distort these numbers?

The first is mixing time periods. If you count marketing spend for one quarter but customers won over a different window, CAC swings for reasons that have nothing to do with performance. Match the spend window to the customer window, and for long sales cycles consider lagging spend by your typical time to close.

The second is ignoring cohorts. A blended churn rate mixes old, loyal customers with new ones who may leave faster. Calculate retention by the month customers joined, and LTV estimates become far more reliable.

The third is treating LTV as cash in the bank. LTV is earned over years; CAC is spent now. That is why payback matters: a business with a strong ratio but a two-year payback can still run out of money while it grows.

The fourth is measuring channels on platform-reported conversions. Ad platforms tend to credit themselves for sales that would have happened anyway, which makes their CAC look lower than it is. Tie spend to real revenue in your own data, and where you can, check the biggest channels with an incrementality test.

• Match spend and customer windows.
• Use cohorts for churn and LTV.
• Track payback in months alongside the ratio.
• Check platform-reported CAC against your own revenue data.

How do you improve the numbers?

There are four levers. Lower CAC by moving budget to the channels and segments that convert best, which needs measurement that ties spend to revenue rather than to clicks. Raise revenue per customer through pricing and expansion. Raise margin. And lower churn, which lifts LTV more than almost anything else because it sits in the denominator.

The first lever is where marketing has the most direct control, and it is the reason I tie spend to revenue, LTV and payback in my own work: budget decisions get better when every channel is judged on what it returns, not on what it reports.

Revisit the numbers every quarter and whenever pricing, churn or the channel mix changes. Present them per channel to whoever owns the budget, with the payback in months next to each one, so the conversation moves from which channel reports the most conversions to which channel returns its cost fastest. That framing makes it much easier to move money away from a channel that looks busy but pays back slowly, and towards one that quietly earns its keep.

• Calculate CAC and payback per channel, not only blended.
• Include salaries and tools in CAC.
• Use gross margin in LTV.
• Watch payback in months; cash is spent long before LTV is earned.