Ecommerce Customer Acquisition Cost: What CAC Is and How to Calculate It

Customer acquisition cost, usually shortened to CAC, answers one of the most important questions in ecommerce:

How much does it cost us to acquire a new customer?

That sounds straightforward.

Spend $10,000 on advertising. Acquire 200 new customers. CAC is $50.

But the calculation is the easy part.

The harder questions are:

• Is $50 a good CAC?
• Can the business afford it?
• Does CAC change as you increase spend?
• Should repeat purchases influence what you are willing to pay?
• Is the platform actually acquiring new customers, or generating revenue from people who already know the brand?
• What happens to profit after the acquisition cost is paid?

There is no universal good CAC for ecommerce.

A $25 CAC can be terrible for one brand.

A $150 CAC can be excellent for another.

The right number depends on what the customer is worth to the business.

What is customer acquisition cost in ecommerce?

Customer acquisition cost measures how much a business spends to acquire a new customer.

Shopify currently defines CAC as the amount spent on advertising and sales divided by the number of first-time customers attributed to the campaign.

That distinction matters.

CAC is about customers, not orders.

If an existing customer comes back and places their fifth order, that is revenue.

It is not a new customer acquisition.

The basic formula is:

CAC = customer acquisition spend ÷ new customers acquired

For example:

Advertising spend: $20,000

New customers acquired: 400

CAC:

$20,000 ÷ 400 = $50

The business spent an average of $50 to acquire each new customer.

Simple enough.

Now we need to figure out whether that was actually good.

What is a good ecommerce CAC?

There is no universal answer.

A good CAC depends on factors including:

• average order value
• gross margin
• contribution margin
• product mix
• shipping and fulfillment costs
• discounts
• payment fees
• return rates
• repeat purchase behavior
• customer lifetime value
• cash flow
• growth objectives

If you sell a $40 product with a low margin, a $50 CAC may be impossible to support.

If you sell a $400 product with healthy margins, a $50 CAC may be extremely attractive.

This is why comparing CAC between unrelated ecommerce brands is usually not very useful.

The better question is:

How much can we afford to pay for a new customer given our economics?

That number is your allowable CAC.

How to calculate customer acquisition cost

Let’s start with a simple example.

An ecommerce brand spends:

Google Ads: $30,000

Meta Ads: $20,000

Total paid media spend: $50,000

Those campaigns generate 1,000 new customers.

CAC:

$50,000 ÷ 1,000 = $50

The blended paid CAC is $50.

But there are already some decisions hiding underneath that number.

Maybe Google acquired customers for $40.

Meta acquired them for $65.

Maybe one channel generated higher-value customers.

Maybe one generated a much higher first-order AOV.

Maybe one looks stronger only because its attribution system is claiming more customers.

The formula is simple.

The analysis should not stop there.

CAC vs CPA: what is the difference?

CAC and CPA are often used interchangeably.

They can mean different things.

CAC specifically refers to the cost of acquiring a new customer.

CPA, or cost per acquisition/action, can refer to the cost of generating whatever conversion action the campaign is optimizing toward.

That might be:

• a purchase
• a lead
• a subscription
• a signup
• an app install

For ecommerce, a purchase CPA can include purchases from both new and returning customers.

CAC should focus on first-time customers.

Shopify separates first-time and returning customers in its current marketing reporting, alongside metrics such as CPA, ROAS, AOV, and conversion rate.

That makes the distinction useful for growing brands.

If your objective is acquiring more customers, knowing the cost per order is not enough.

You need to know how much it costs to acquire somebody genuinely new.

Why CAC can tell you something ROAS cannot

Suppose a campaign spends $10,000.

It generates $50,000 in attributed revenue.

ROAS is:

5x

Sounds good.

But consider two scenarios.

Scenario A

New customers: 250

CAC: $40

Scenario B

New customers: 50

CAC: $200

The campaign reports the same ROAS in both cases.

The acquisition story is completely different.

Scenario B may simply be generating a large amount of revenue from existing customers.

That is not necessarily bad.

Returning-customer revenue is valuable.

But if the objective is growth through customer acquisition, ROAS alone does not tell you whether that is happening.

Related: What Is ROAS in Ecommerce? How to Calculate It and What It Really Tells You

What is allowable CAC?

Allowable CAC is the amount your business can afford to spend to acquire a new customer while still meeting its economic objectives.

To estimate it, start with the economics of the order.

Suppose you sell a product for:

$120

Now subtract variable costs.

Product cost: $35

Fulfillment: $8

Payment fees: $4

Shipping subsidy: $10

Discounts: $3

That leaves:

$60 contribution before advertising

If the business wants to generate $20 in contribution from the first order after acquisition cost, the allowable first-order CAC would be:

$40

Spend more than $40 and the first order falls below that contribution target.

Spend less and the first order produces more contribution.

That is far more useful than saying:

“Our industry usually pays around $35 per customer.”

Your business economics determine what you can afford.

First-order CAC vs lifetime CAC

This is where the discussion becomes more nuanced.

Some ecommerce businesses need the first order to be profitable.

Others are comfortable acquiring customers at breakeven or even at a small first-order loss because customers reliably purchase again.

Imagine two brands.

Brand A

First order contribution before acquisition: $50

Repeat purchase rate: low

Allowable CAC may need to stay well below $50.

Brand B

First order contribution before acquisition: $50

Customers regularly purchase again over the next 12 months.

Brand B may rationally spend more to acquire the customer because the customer is worth more than the first transaction.

That is where customer lifetime value enters the conversation.

Should you use lifetime value to set CAC?

Yes, but carefully.

Lifetime value can help determine how aggressively a brand should acquire customers.

The problem is that optimistic LTV assumptions can make almost any CAC look acceptable.

For example:

CAC: $80

First-order contribution: $45

Projected lifetime contribution: $200

That might be an attractive acquisition.

But only if the $200 is supported by actual customer behavior.

Ask:

• What percentage of customers purchase again?
• How soon?
• How many times?
• What is the margin on repeat orders?
• Does retention vary by acquisition source?
• Does retention vary by first product purchased?
• Are you using actual cohort data or assumptions?

Do not spend projected lifetime value before you have evidence that it exists.

CAC usually changes as you scale

This is one of the most important realities in paid ecommerce growth.

Suppose a brand spends $10,000 per month and acquires customers at:

$35 CAC

It may be tempting to assume:

Spend $50,000 and acquire five times as many customers at $35 each.

That often does not happen.

At lower spend, advertising platforms can concentrate investment on the easiest available opportunities.

As spend increases, they may need to reach:

• broader audiences
• less obvious buyers
• lower-intent searches
• customers earlier in their journey

CAC can rise.

That does not automatically mean scaling is failing.

The question is whether the marginal CAC remains acceptable.

What is marginal CAC?

Marginal CAC asks:

What did the additional customers cost us?

Suppose:

Before scaling

Spend: $50,000

New customers: 1,250

Average CAC: $40

Now increase spend.

After scaling

Spend: $70,000

New customers: 1,550

Overall CAC:

$70,000 ÷ 1,550 = $45.16

But look at the incremental spend.

Additional spend:

$20,000

Additional customers:

300

Marginal CAC:

$20,000 ÷ 300 = $66.67

The account average looks like roughly $45 CAC.

The newest customers cost almost $67.

That is incredibly useful information when deciding whether to keep scaling.

A rising CAC is not automatically bad

Imagine your allowable CAC is $80.

You are currently acquiring customers at $40.

You increase spend.

CAC rises to $55.

Should you panic?

Probably not based on that information alone.

The acquisition became less efficient.

But it may still be comfortably attractive.

If the business can acquire substantially more customers at $55 while maintaining healthy contribution, accepting a higher CAC may generate more total profit.

This is similar to the ROAS problem.

Brands can sometimes make efficiency metrics look excellent simply by spending less.

That does not necessarily maximize growth.

The goal is not the lowest possible CAC

A $20 CAC sounds better than a $40 CAC.

But consider this:

Scenario A

Spend: $10,000

New customers: 500

CAC: $20

Scenario B

Spend: $50,000

New customers: 1,250

CAC: $40

Scenario A has better CAC.

Scenario B acquires 750 more customers.

If the business can comfortably afford $40 CAC, Scenario B may be much more valuable.

The objective is not:

Acquire customers at the lowest possible cost.

It is:

Acquire as many valuable customers as the business can support at acceptable economics.

That is a much better paid growth objective.

Blended CAC vs channel CAC

Ecommerce businesses should usually look at CAC from more than one angle.

Channel CAC

How much does a particular channel report spending to acquire customers?

Examples:

Google CAC: $42

Meta CAC: $56

Blended CAC

How much did the business spend across acquisition channels relative to total new customers?

For example:

Google spend: $40,000

Meta spend: $35,000

Other paid acquisition: $5,000

Total spend: $80,000

Total new customers: 1,600

Blended CAC:

$50

Blended CAC provides a useful business-level view because it does not require every platform to agree on attribution.

Why platform CAC and business CAC may disagree

The same attribution issues that affect ROAS also affect CAC.

Imagine a customer:

1. Sees a Meta ad.
2. Clicks.
3. Leaves.
4. Searches the brand on Google.
5. Clicks a Shopping ad.
6. Purchases.

Meta may associate the customer with its campaign.

Google may do the same.

Shopify may report the customer journey differently.

There was still only one new customer.

That is why platform-level CAC should be useful for optimization, while blended business-level CAC provides another layer of accountability.

Related: Ecommerce Attribution: Why Google Ads, Meta and Shopify Never Agree

Google Ads can optimize toward new customers

Google currently provides customer acquisition goals that allow eligible campaigns to place additional value on new customers or focus specifically on new-customer acquisition.

Google also reports customer acquisition cost for supported lifecycle-goal campaigns as ad spend allocated to new customers divided by the number of unique new customers acquired.

That can be useful for ecommerce brands trying to distinguish total conversion value from actual customer growth.

But there is an important strategic question before turning the setting on:

What is a new customer worth?

If that value is wrong, the bidding system is optimizing around a bad business assumption.

Google itself recommends thinking about new-customer value relative to expected customer value rather than treating every first purchase identically.

Product mix can change allowable CAC

Not every customer is economically equal.

Suppose you sell two products.

Product A

AOV: $70

Contribution before acquisition: $25

Repeat rate: low

Product B

AOV: $160

Contribution before acquisition: $75

Strong repeat behavior

A customer acquired through Product B may be worth substantially more.

That can justify different acquisition economics.

For ecommerce brands with larger catalogs, this is one reason product-level media analysis matters.

Advertising should connect to merchandising and product economics.

Not every SKU deserves the same CAC target.

AOV affects CAC, but it is not the whole story

Increasing average order value can give the business more room to acquire customers.

Suppose CAC is:

$50

At an $80 AOV, that may be difficult.

At a $160 AOV, it may be much more manageable.

But only if the higher order value also produces healthy margin.

AOV can increase because:

• customers buy more products
• bundles perform well
• premium products sell
• discounts change
• product mix shifts

Always connect AOV back to contribution.

Related: How to Increase Average Order Value Without Relying on Bigger Discounts

Conversion rate affects how much customers cost

CAC is partly determined after the click.

Imagine two stores buying traffic at exactly the same cost.

Both get:

10,000 paid sessions

Both spend:

$20,000

Store A

Conversion rate: 2%

Orders: 200

Store B

Conversion rate: 3%

Orders: 300

Assuming the same new-customer mix, Store B has considerably better acquisition economics despite buying traffic at the same price.

This is why improving paid media does not always mean changing the advertising account.

Sometimes the best CAC opportunity is:

• a stronger product page
• better mobile UX
• a better offer
• clearer shipping
• stronger merchandising
• a smoother checkout

Paid acquisition and CRO are connected.

Related: Ecommerce Conversion Rate Optimization: What CRO Is and Why It Matters

What metrics should you watch alongside CAC?

CAC becomes much more useful when paired with other ecommerce metrics.

Average order value

How much revenue does the initial order generate?

Contribution margin

How much remains after variable costs?

ROAS

How much attributed revenue does advertising generate relative to spend?

New-customer revenue

How much revenue comes from customers being acquired rather than returning customers?

Repeat purchase rate

How frequently do acquired customers buy again?

Customer lifetime value

How much value does a customer actually generate over time?

MER

How efficiently does total business revenue relate to total marketing investment?

Conversion rate

How effectively does traffic turn into purchases?

You do not need a dashboard with 70 metrics.

But CAC should not live alone.

Common ecommerce CAC mistakes

Using total orders instead of new customers

If your objective is customer acquisition, repeat orders should not count as newly acquired customers.

Treating every customer as equally valuable

Product, margin, first-order size, and repeat behavior can vary.

Setting CAC targets from industry benchmarks

Your allowable CAC should come from your economics.

Using optimistic lifetime value assumptions

Observed behavior is much safer than a best-case spreadsheet.

Panicking when CAC rises during scaling

A higher CAC can still represent excellent growth if it remains below your allowable threshold.

Focusing only on platform-reported CAC

Compare advertising-platform data with Shopify and business-level reporting.

Ignoring contribution margin

A cheap customer who produces no contribution is not necessarily a good customer.

Trying to minimize CAC at all costs

This can lead to underspending and missed profitable growth.

How should a growing ecommerce brand set a CAC target?

A practical process looks like this.

Step 1: Understand first-order

‍