CAC vs CPA vs LTV: What a Customer Is Really Worth

Three numbers, three questions

Advertising reports are full of acronyms, but three of them answer the questions that decide whether a business grows or burns money:

CPA: the cost of one action

CPA = ad spend ÷ number of actions. The action is whatever the campaign was bought for: a sign-up, an install, a subscriber, a completed task. If you spend $300 and get 600 sign-ups, your CPA is $0.50.

CPA is the number you control most directly, because it is what you bid or pay per result. But an action is not yet a customer, so a low CPA alone does not prove a campaign is profitable. CPM vs CPC vs CPA compares it with the other pricing models.

CAC: the cost of one customer

CAC = total sales and marketing costs ÷ new paying customers. It includes ad spend, but also tools, agency fees, and the share of salaries spent on winning customers. If you spend $3,000 in a month and win 60 new paying customers, your CAC is $50.

Two versions are useful. Paid CAC counts only ad spend and customers from paid channels, and tells you whether advertising works. Blended CAC counts all costs and all new customers, including those from search, word of mouth, and referrals, and tells you whether the business works.

LTV: what a customer is worth

LTV = average gross profit per customer per month × average months a customer stays. Use gross profit, not revenue, because product costs, payment fees, and refunds are not yours to spend on acquisition. For subscriptions, the average lifetime in months is roughly 1 ÷ monthly churn rate.

For apps, games, and shops without a subscription, estimate LTV from real cohorts: take everyone who joined in one month and add up the profit they brought over 90 or 180 days. That is more reliable than a formula built on assumptions.

The LTV to CAC ratio

Dividing LTV by CAC shows how much each dollar spent on winning a customer brings back over that customer’s life. A widely used rule of thumb is 3 to 1 or better:

• Below 1: every new customer loses money. Stop and fix pricing, retention, or acquisition.
• Around 1 to 3: customers pay for themselves, but there is little left for everything else.
• 3 or more: healthy for most businesses.
• Far above 5: you may be growing too slowly and could afford to spend more.

The right target depends on your cash position and growth plans, so treat 3 to 1 as a starting point, not a law.

Payback period

Payback period = CAC ÷ monthly gross profit per customer. In the example above, a CAC of $50 and $14 profit a month means a customer has repaid their cost after about 3.6 months. Even with a good LTV to CAC ratio, a long payback period ties up cash, which matters most for small businesses. Many aim to earn back CAC within twelve months.

From LTV to the bid you can afford

This is where the three numbers meet. Start from LTV, decide your target ratio, and work down the funnel to the action you pay for:

1. Maximum CAC = LTV ÷ target ratio.
2. Conversion rate = share of actions that become paying customers.
3. Maximum CPA = maximum CAC × conversion rate.

The same logic works with ROAS. What is ROAS? shows how to turn a target return on ad spend into a maximum CPA.

Common mistakes

• Using revenue instead of profit for LTV, which makes every campaign look better than it is.
• Guessing lifetime for a new business. Use cautious numbers until real cohorts exist, and update them every few months.
• Ignoring refunds and chargebacks, which reduce LTV quietly.
• Mixing channels. A blended CAC can hide one channel that loses money behind another that does well.
• Counting actions as customers. A cheap CPA from users who never pay is not a cheap CAC.

Using these numbers on Sharklio

On Sharklio, your bid is your CPA: you pay a fixed price for each approved completion, set separately for each country. Work out your maximum CPA per country with the steps above, enter it as the bid, and you know before the campaign starts that every approved result fits your economics. You can lower bids where results convert less well and raise them where customers are worth more. Read Set bids by country and Pay only for approved results. Sharklio is launching soon.

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