eCommerce GrowthMarketing StrategyAnalytics

Customer Acquisition Cost (CAC): Definition and Formula

First published Nov 10, 2026Updated November 10, 2026

Valentin Radu

Founder & CEO, Omniconvert

Published: Nov 10, 2026Updated: Nov 10, 2026

Reviewed by Cristina Stefanova, Head of Content

A brass kitchen scale holds a single wrapped parcel on one pan and a small stack of coins on the other in a white studio

Quick Answer

Customer acquisition cost (CAC) is the total you spend to win one new customer, found by dividing acquisition spend by the number of new customers won in the same period. For an eCommerce store the open question is the numerator. Some teams count ad spend only. Others add creative, tools, agency fees and salaries. Both versions are valid if you name which one you use. Blended CAC covers all channels and all new customers, and paid CAC covers paid media only. CAC is not CPA, which prices any action. CAC alone misleads, so read it against customer lifetime value and margin.

Key Takeaways

Customer acquisition cost is acquisition spend divided by new customers won in the same period.
The numerator has two common versions: ad spend only, or fully loaded with creative, tools, agency fees and salaries.
Blended CAC uses all new customers and all spend. Paid CAC uses paid media and the customers it brought in.
CAC prices a new customer. CPA prices any action, so a repeat purchase can lower CPA without changing CAC.
A CAC figure has no meaning without customer lifetime value and margin next to it.
Always label which CAC you report, because two correct figures can differ by a wide margin.

Customer acquisition cost is the number every eCommerce team quotes and few define the same way. Two people can say "our CAC is on target" and mean figures that differ by a wide margin. Here are the definition, the formula and the choices hidden inside it.

After 13 years in eCommerce, I know one habit across thousands of brands: CAC is reported without a label. The label says what you counted and which customers you counted. Omniconvert Commander (formerly Nexus) is the AI eCommerce growth engine for Shopify brands: it reads your store, ad and customer data, ranks growth opportunities by profit impact, and builds the campaigns to act on them, and you approve what goes live.

What is customer acquisition cost?

Customer acquisition cost (CAC) is the total you spend to win one new customer. You divide acquisition spend by the number of new customers won in the same period. It prices a customer, not a click or a sale.

Customer acquisition cost is defined as the total acquisition spend in a period divided by the number of first-time customers won in that period. A repeat buyer does not count, because you did not acquire them again.

For the full playbook on bringing the number down, read how to reduce customer acquisition cost in eCommerce.

What is the CAC formula?

CAC equals total acquisition spend divided by new customers acquired in the same period. Use identical dates for both numbers and count first-time customers only. A month is a common window. The choices sit in what you count as spend.

Take a month. Add up what you chose to count as acquisition spend. Divide by the first-time customers from your store data for that month. If you counted 10,000 in spend and won 200 first-time customers, CAC is 50 (these numbers are for illustration only).

Match the windows. Customers who buy this month often saw an ad last month. If your buyers take long to decide, compare spend in one period with customers in the next, and name that lag.

What goes into the CAC numerator?

Two versions are in use. Ad-spend-only CAC counts media cost alone and suits channel decisions. Fully loaded CAC adds creative, tools, agency fees and salaries, and suits profit and investor discussions. Mixing them across reports is the error.

Use ad-spend-only CAC to decide where the next budget goes. Use fully loaded CAC when you ask whether acquisition pays. Creative, tools, agency retainers and acquisition salaries are real costs of winning a customer.

The two figures answer different questions. One asks which channel is cheaper. The other asks whether growth pays. Report both, and label each.

Blended CAC versus paid CAC: which one do you use?

Blended CAC divides all acquisition spend by all new customers, whatever the channel. Paid CAC divides paid media spend by the new customers that paid media brought in. Blended is steadier and harder to game. Paid shows channel health but depends on attribution.

Blended CAC is defined as total acquisition spend divided by every new customer, including those who arrived through organic search, email or word of mouth. Paid CAC isolates the ad channels, so it is only as good as the attribution behind it. If you want the wider picture of what your reports can and cannot see, read the Shopify analytics guide.

Source: Omniconvert, the CAC variants and when each one fits
Variant	Numerator	Denominator	Best use
Ad-spend CAC	Media spend only	First-time customers	Channel and budget calls
Fully loaded CAC	Media, creative, tools, agency, salaries	First-time customers	Profit and investor review
Blended CAC	All acquisition spend	All new customers, any channel	Whole-business trend
Paid CAC	Paid media spend	New customers credited to paid	Ad channel health

Monday meeting: the ad manager shows paid CAC from the ad platform, down for three weeks. The finance lead shows blended CAC from the sheet, up. Both numbers are right and both look reasonable alone. The team spends the hour debating attribution, and the budget decision waits another week. One labelled definition ends the argument.

How is CAC different from CPA?

CAC is the cost of one new customer. CPA is the cost of one chosen action, such as a purchase or a lead. A returning buyer adds to CPA but never to CAC. For a store with strong repeat sales, CPA can look healthy while CAC is high.

Teams swap the two terms. Keep them apart. CPA prices an action, and the live cost per acquisition (CPA) page defines it in full. CAC prices a person you did not have before.

Why does CAC mislead without lifetime value?

CAC says what a customer cost. It does not say what the customer returns. A high CAC can be sound when customers buy again and a low CAC can lose money when they never do. Read CAC next to customer lifetime value and margin before you judge it.

Pair CAC with customer lifetime value. The usual step is the LTV to CAC ratio, and the time it takes to earn the spend back is the CAC payback period. For a profit view, see POAS.

Testing lifts the return on traffic you already pay for. Explore data shows a 23.2% average conversion uplift across 70,000+ experiments [Omniconvert Explore, 70,000+ experiments]. That is an average across tests, not a forecast. One example of a testing programme at work: AliveCor used Omniconvert to run a structured A/B testing programme and achieved +21% conversion rate, +5% revenue per visitor, and 94% statistical relevance across their experiments. [Omniconvert, AliveCor case study]

To bring CAC down, lift conversion on traffic you already buy, target lookalikes of your best customers and win repeat orders. The reduce CAC solution page covers the approach, and customer acquisition strategy the plan. For software, see the best tools to lower CAC on Shopify. To see which arguments rival brands use to win customers, read competitor ad intelligence.

Customer acquisition cost: FAQs

What is customer acquisition cost?

Customer acquisition cost (CAC) is the total you spend to win one new customer in a period. Divide acquisition spend by the number of new customers won in that same period.

What is the CAC formula?

CAC equals total acquisition spend divided by new customers acquired in the same period. Use the same dates for both numbers, and count first-time customers only.

How do I calculate CAC for a Shopify store?

Pick a period, such as a month. Add the acquisition costs you have chosen to count. Divide by first-time customers from your store data for that month. Compute a blended figure and a paid figure.

What is the difference between blended CAC and paid CAC?

Blended CAC divides all acquisition spend by all new customers, whatever the channel. Paid CAC divides paid media spend by the new customers that paid media brought in. Blended is more stable. Paid is more exposed to attribution error.

What is the difference between CAC and CPA?

CPA is the cost of any chosen action, such as a purchase or a lead. CAC is the cost of a new customer. A repeat buyer can add to CPA but never to CAC.

Is a low CAC always good?

No. A low CAC with low customer value can still lose money. Read CAC next to customer lifetime value and margin, then decide whether a customer repays the spend.

How does Omniconvert Commander relate to CAC?

Omniconvert Commander reads your store, ad and customer data and measures results in True Profit per ad. Use it to check whether the customers behind your CAC repay the spend. You approve what goes live.

Label your CAC

Customer acquisition cost is spend divided by new customers, and the label matters more than the arithmetic. Say whether the numerator is ad spend or fully loaded, and whether the figure is blended or paid. Then read it next to lifetime value and margin. A labelled CAC supports a budget decision. A bare CAC starts an argument.