CAC cost: customer acquisition cost formula and calculator

CAC calculator with payback

The calculator divides your costs by your new customers and puts the result next to the contribution margin of the first order. You see right away whether a new customer pays for themselves or only makes money through repeat purchases. The example values are preset. Enter your own.

CAC formula and example

The formula is short. The work sits in the two numbers you put into it:

A store spends $20,000 a month on ads and pays another $5,000 for agency, creative and tools. In the same month, 400 people order for the first time. Depending on which costs you include, you get two values:

Use paid CAC to compare channels and campaigns. For the question whether your growth makes money, blended CAC is the one that counts, because you pay the agency and the creative team either way.

Which costs belong in CAC

CAC includes everything you spend to get people to buy for the first time. Costs for customers you already have stay out.

Leave out fees and creative and your CAC in the example looks 20% better than it is. Teams that calculate this way scale campaigns that cannot carry their full cost.

Why you divide by new customers only

The most common mistake sits in the denominator. In the example month, 1,000 customers buy, and 600 of them have ordered before. Divide $25,000 by all 1,000 buyers and you get $25 per customer.

1. Wrong: $25,000 ÷ 1,000 buyers = $25. The first order brings $32 in contribution margin, so everything looks profitable.
2. Right: $25,000 ÷ 400 new customers = $62.50. The first order covers only about half of it.

You would have won most of those returning buyers without ads. Your store backend knows who orders for the first time. Count new customers there.

How high can your CAC go?

The first ceiling is the contribution margin of the first order. If your CAC sits below it, you make money on the first purchase. If it sits above, you pre-finance the customer and need repeat orders.

The second ceiling comes from customer lifetime value. If a customer orders 2.5 times at $80 with 40% contribution margin, they bring $80 in contribution margin over their lifetime. How much of that you can spend on acquisition, you work out with the LTV CAC calculator.

Set the ceiling with contribution margin. A $62.50 CAC sounds harmless next to an $80 order and still costs you $30.50 on the first purchase.

Marginal CAC: what your last new customers cost

The average hides what extra budget buys you. The first dollars win the cheapest customers, and each additional dollar gets more expensive. Check marginal CAC before you raise a budget:

The average rises by only $5.88. The extra $5,000 buys 60 new customers, though, at $83.33 each. With $32 in first-order contribution margin, each of them needs 2.6 orders to pay back.

Measuring CAC in Google Ads

Google Ads shows you cost per conversion. That figure divides cost by all purchases, including those from returning customers, so it almost always sits below your real CAC.

The customer acquisition goal lets Google Ads bid higher for new customers or show ads to new customers only. Google tells existing customers apart using the customer lists and website tag data you provide. The setting shifts budget toward new customers. You still count them in your store.

To compare channels, you need a paid CAC per channel. Assign each new customer to the channel of their first order, through UTM parameters or the source field in your store backend. When channels differ a lot, move budget to the cheaper one as long as its marginal CAC stays below your ceiling. Check order values too: a channel with a higher CAC can bring bigger first orders and still come out ahead.

For a view across all channels at once, set your total marketing spend against total revenue with the marketing efficiency ratio. To read the same ads as a revenue metric, use the ROAS formula calculator.

Lower your CAC without cutting budget

You lower CAC in two ways: less cost per new customer, or more new customers from the same cost. These levers work hardest in ecommerce:

• Stop brand waste: Searches for your brand name often come from existing customers. Split brand and non-brand so budget reaches new buyers.
• Allocate budget by contribution margin: High-margin products can carry a higher CAC. Steer feeds and campaigns by margin per product.
• Raise conversion rate: When more visitors buy from the same traffic, CAC drops directly. Product pages, bundles and checkout are the levers.
• Build repeat purchases: Retention does not lower CAC. It raises the ceiling you can afford.

That is how we work as an agency for Google Ads with ecommerce brands. Two examples of how acquisition cost changed along the way:

$100,000 to around $600,000 monthly revenue.

Acquisition cost $220 → $100

+30% revenue in 3 months.

Acquisition cost −35%