How to Calculate Customer Acquisition Cost (CAC) Correctly

Customer acquisition cost (CAC) is what you spend to win one new customer. The correct formula for an online store is: CAC = total acquisition spend in a period / new customers acquired in the same period. “Total acquisition spend” means ad spend plus the other costs you pay to bring in first-time buyers, such as agency fees and influencer product. “New customers” means people who placed their first order, not all orders.

Most small stores get CAC wrong in one of two ways. They divide ad spend by every order, which mixes in repeat buyers and makes CAC look cheap. Or they copy the cost per conversion from Meta or Google, which counts purchases, not new people. This guide shows the formula, a worked month with four ways to calculate it, how CAC differs from CPA and blended ROAS, and where Shopify and Google Ads now report CAC for you.

What belongs in CAC, and what does not

CAC answers one question: what did it cost to get a person to buy from you for the first time? So the top line should hold every cost you would stop paying if you stopped acquiring customers, and nothing else.

Cost Include in CAC? Why

Ad spend aimed at new buyers (Meta, Google, TikTok, Pinterest) Yes The core of acquisition spend.

Agency or freelancer fees for running those ads Yes You pay them to win customers.

Influencer fees, gifted product and its shipping Yes Acquisition spend paid in product instead of cash.

Affiliate commissions on first orders Yes Paid only when a new buyer arrives.

Welcome discount on first orders Pick one place Either subtract it from first-order profit or add it to CAC. Never both.

Email and SMS tools used for existing customers No Retention cost, not acquisition.

Shopify plan, apps, your own salary No Fixed costs. They belong in your monthly profit and loss.

Product cost, shipping, payment fees No Order costs. They reduce profit per order, which you compare against CAC.

A practical split for a small store. Your own costs may sort differently; the rule is to count each cost once.

The bottom line matters as much. Count unique new customers who placed a first order in the period. Shopify defines a first-time customer as “a customer who placed their first order with your store”, and a returning customer as one “whose order history already includes at least one order.” Use the same definition every month.

CAC vs CPA vs blended ROAS

These three numbers use some of the same inputs, so they get confused. They answer different questions.

CPA (cost per acquisition, or cost per conversion) is cost divided by conversions. Google Ads defines “Cost / conv.” as your total cost divided by the number in the “Conversions” column. A conversion is any tracked purchase, so a repeat buyer who clicks an ad counts. Google also suggests counting “Every” conversion for sales, so one person can produce several.
CAC divides cost by unique new customers. It is usually higher than a platform CPA built on the same spend, because new customers are only part of all purchases.
Blended ROAS (some operators call it MER, marketing efficiency ratio) is total store revenue divided by total ad spend. It includes revenue from returning customers you did not pay to reacquire, so it can look healthy while new-customer economics are weak.

Use CPA to manage a single campaign inside an ad platform. Use CAC to decide whether acquiring customers makes money. Use blended ROAS as a quick health check on the whole store, not as proof that ads pay. Our guide to the ROAS you need to break even shows the per-order version of that check.

Worked example: one month, four CAC numbers

All numbers in this section are hypothetical. They describe one month at a small US store selling a $60 product, the same modelled store used in our customer lifetime value guide.

Meta ad spend: $4,200. Meta reports 210 purchases.
Google Ads spend: $2,600. Google reports 160 conversions.
Influencer gifting (product cost plus shipping): $450.
Freelance ads manager: $800.
Store orders in Shopify: 520, of which 300 were first orders from new customers and 220 were repeat orders.
New customers paid $54 (a 10% welcome discount). Repeat orders paid $60.

Notice that Meta and Google together claim 370 purchases while the store has only 300 new customers. Each platform counts conversions under its own attribution rules, so the same order can be claimed twice, and repeat buyers are included. Platform numbers are a starting point, not the denominator for CAC.

Method Calculation Result Verdict

Meta cost per purchase $4,200 / 210 $20.00 Platform CPA, includes repeat buyers and overlap

Google cost per conversion $2,600 / 160 $16.25 Platform CPA, same problems

Ad spend per order $6,800 / 520 orders $13.08 Wrong: counts repeat orders as acquisitions

Ad spend per new customer $6,800 / 300 $22.67 Paid media CAC, leaves out other acquisition costs

Fully loaded CAC $8,050 / 300 $26.83 The number to plan with

Paid-channel CAC ($6,800 + $800) / 230 paid new customers $33.04 What paid ads cost per customer they actually brought in

Hypothetical store, one month. All results rounded to the cent. Calculated in python twice: once with exact decimal arithmetic and once from a row-by-row order ledger.

The last row needs one extra assumption. Suppose Shopify’s marketing reports attribute 230 of the 300 new customers to paid channels, and the other 70 came from search, social posts, referrals or word of mouth. Those 70 would likely have arrived without the ads. If you divide ad spend and the ads manager’s fee by the 230 customers the ads brought in, paid CAC is $33.04, not $22.67.

Same store, same month, and CAC ranges from $13.08 to $33.04 depending on the method. Whoever reports the lowest figure is usually the one dividing by the wrong thing.

Is $26.83 good or bad?

CAC on its own means nothing. Compare it with the profit a new customer brings. In the CLV model, a discounted first order leaves $19.51 of contribution after product cost ($24), shipping and packing ($7), a 2.9% + 30 cent card fee and a 3% returns allowance. That card rate is the US Shopify Basic online rate with Shopify Payments, as listed on Shopify’s pricing page on November 1, 2026. Over 12 months, the modelled customer is worth $31.59 in profit.

CAC method CAC Profit on first order ($19.51) 12-month profit ($31.59) / CAC Pays back within

Ad spend per order $13.08 +$6.43 2.42 First order

Ad spend per new customer $22.67 -$3.16 1.39 Within 3 months

Fully loaded CAC $26.83 -$7.32 1.18 Within 6 months

Paid-channel CAC $33.04 -$13.53 0.96 Not within 12 months

Modelled. Payback months come from the cumulative cohort in the CLV guide (profit per customer of $24.29 by month 3, $27.31 by month 6 and $31.59 by month 12).

This is why the method matters. The per-order version says ads pay back on the first sale. The fully loaded version says you wait up to six months for each new customer to cover what you paid for them. The paid-channel version says the ads themselves do not earn their money back inside a year. All three describe the same month.

Blended ROAS hides this. Store revenue was $29,400 ($16,200 from new customers and $13,200 from repeat orders) against $6,800 of ad spend, a blended ROAS of 4.32. That looks strong, but $13,200 of it came from customers the store already had.

The discount trap: count it once

A welcome discount is a real acquisition cost. You can handle it in either of two places, and both give nearly the same answer:

Option A: leave CAC at $26.83 and use the discounted first-order profit of $19.51. Gap: $7.32 per customer.
Option B: add the $6 discount to CAC ($1,800 across 300 customers, making CAC $32.83) and compare with full-price first-order profit of $25.16. Gap: $7.67.

The 35 cent difference comes from the card fee and returns allowance, which shrink slightly on a cheaper order. What you must not do is add the discount to CAC and also use the discounted first-order profit. That counts the same $6 twice and makes acquisition look worse than it is.

Where Shopify and Google Ads report CAC

Both platforms now show a CAC figure. Neither is a full replacement for your own calculation. Checked November 1, 2026.

Shopify

From your Shopify admin, go to Analytics > Reports, then filter the category to Marketing.
Open Performance by marketing channel. Shopify lists its metrics as “Ad spend, return on ad spend (ROAS), cost per acquisition (CPA), and customer acquisition cost (CAC).” By default it shows the last 30 days using the last non-direct click attribution model.
Read the cost caveat. Shopify says spend-based metrics apply only to marketing channels that report cost data to Shopify, such as a connected ad platform. A dash means no cost data, which is not the same as zero.
For the denominator, the Customers category has a New customers over time report and a New vs returning customers report.

Shopify’s report cannot see your agency invoice, influencer product or any ad platform that does not send cost data. Treat its CAC as a paid media figure for connected channels. Our walkthrough of the Shopify Analytics reports that matter covers the other weekly reports.

Google Ads

If you turn on a customer acquisition goal in Google Ads, you get new customer columns. Google defines its CAC column as “The ad spend allocated to new customers divided by the total of unique new customers acquired through a campaign.” You can also segment the Campaigns table by “New vs. returning customers”.

Google says these metrics are only available if you have activated the lifecycle goal in the campaign and are optimizing toward Purchase conversions, and the reporting is not available retroactively.
Without your own data, Google treats someone as new if they have not purchased within the last 540 days. You can override this by sending a new_customer value (true or false) in your Google Ads conversion tag, or customer_type (“new” or “returning”) through Google Analytics.
Google says CAC columns are unavailable for Demand Gen campaigns. For those, divide total cost by new conversions yourself.
The customer acquisition goal works with Search, Performance Max, Shopping and Demand Gen campaigns, and Google recommends the “New Customer Value” setting for all advertisers with purchase conversion goals.

Google’s CAC covers Google spend only, and the 540-day window will not match Shopify’s “first order ever” definition. Expect the two to differ. If you run Shopping or Performance Max, our guide to when Performance Max works and when it wastes money explains how to read its reports.

How to calculate your own CAC each month

Pick the period. A calendar month works for most small stores. Use the same dates for cost and customers.
Total your acquisition spend. Pull spend from each ad account’s billing or reporting, then add agency fees, influencer costs and affiliate commissions on first orders.
Count new customers. Use Shopify’s New customers over time report for the same dates. Do not use orders or platform conversions.
Divide. That is your fully loaded CAC.
Split paid from unpaid if you can. Use Shopify’s marketing reports to estimate how many new customers came through paid channels, and calculate a paid-channel CAC alongside the blended one.
Compare with profit. Set CAC against first-order contribution and 12-month profit per customer. Our guide to gross margin, contribution margin and net profit shows how to work out contribution.

A note on timing. Google’s main conversion columns are calculated by the time of the click, not the time of the conversion, and Google says reporting can lag 24 to 48 hours. A customer who clicks on March 30 and buys on April 2 may land in March in Google and April in Shopify. Monthly CAC smooths most of this out, but avoid reading CAC week by week on a small store.

Common CAC mistakes

Dividing by orders. Repeat orders were not acquired. In the example this cut CAC from $22.67 to $13.08.
Adding up platform conversions. Meta and Google claimed 370 purchases against 300 new customers.
Leaving out non-ad costs. Agency fees and gifted product added $4.17 per customer here.
Counting the welcome discount twice. Put it in CAC or in first-order profit, not both.
Judging CAC without profit. A $26.83 CAC is fine for a product with $40 of first-order profit and a problem at $19.51.
Trusting a single dashboard. Shopify sees only connected cost data; Google sees only Google. Your spreadsheet sees everything you put in it.

What you should check next

List every acquisition cost you paid last month, including invoices outside the ad platforms.
Pull new customers for the same month from Shopify’s New customers over time report.
Calculate fully loaded CAC and, if you can, paid-channel CAC.
Compare both with first-order contribution and 12-month profit per customer.
If CAC is above first-order profit, decide how long a payback you can fund. If it is above 12-month profit, cut spend or fix margin first. Our guide to Google Ads on a small budget covers where to start.
Recalculate monthly, and whenever you change discounts, agencies or channels.

Frequently asked questions

Is CAC the same as cost per acquisition?

Not in ad platforms. Cost per acquisition, or cost per conversion, divides cost by tracked conversions, which include repeat buyers and can count one person several times. CAC divides cost by unique new customers.

Should CAC include my own time?

For a solo store, most owners leave it out and treat their time as a fixed cost. If you pay someone else to run ads or creator outreach, include that fee.

What is a good CAC for an online store?

There is no universal figure. A good CAC is one comfortably below the profit a new customer brings you over the period you can afford to wait. Compare it with your own first-order and 12-month profit, not an industry average.

Why is Shopify’s CAC different from my calculation?

Shopify’s spend-based metrics only include channels that report cost data to Shopify, and it applies an attribution model to decide which channel gets credit. Your own calculation can include every cost and every new customer.

How often should a small store calculate CAC?

Monthly is enough for most. Weekly numbers on a small store swing with a handful of orders and with reporting lags between platforms.

The takeaway

Divide every acquisition cost by unique new customers in the same period, count discounts once, and judge the result against profit per customer, not revenue. In the modelled store that turns a comfortable-looking $13.08 into a $26.83 CAC that takes up to six months to pay back, which is the number to plan around.

Sources

Shopify Help Center, “Customers reports” (first-time and returning customer definitions, New customers over time, New vs returning customers, admin path), checked November 1, 2026. help.shopify.com
Shopify Help Center, “Marketing reports” (Performance by marketing channel metrics including CPA and CAC, cost data caveat, dash vs zero, default last non-direct click model), checked November 1, 2026. help.shopify.com
Shopify, Pricing (US Basic online card rate 2.9% + 30 cents with Shopify Payments), checked November 1, 2026. shopify.com/pricing
Google Ads Help, “Understand your conversion tracking data” (Cost / conv. definition, Every vs One counting, click-time reporting, 24 to 48 hour lag), checked November 1, 2026. support.google.com
Google Ads Help, “About customer lifecycle goals” (New Customer Value, New Customer Only, eligible campaign types, recommendation), checked November 1, 2026. support.google.com
Google Ads Help, “Measure your lifecycle goals campaigns” (CAC column definition, New vs. returning customers segment, 540-day auto-detection, Demand Gen limitation, no retroactive data), checked November 1, 2026. support.google.com
Google Ads Help, “Set up new customer acquisition parameter in your conversion tracking tag” (new_customer and customer_type values), checked November 1, 2026. support.google.com

Last reviewed: November 1, 2026. The formulas do not change; the Shopify and Google Ads report features and the card rate are as published on that date.

How this article was made: researched and drafted with AI assistance, with every factual claim checked against the sources above. The store, its spend, order counts, 230 paid-channel customers, costs and cohort profits are hypothetical; all tables are modelled from those stated assumptions and are not typical or guaranteed results.

Related guides

Customer lifetime value for small stores: an honest formula
What ROAS do you need to break even?
Gross margin vs contribution margin vs net profit
Meta Advantage+ campaigns for small stores

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