CPA vs CAC: why they are not the same and which one to report

There is a scene that repeats in almost every seller’s monthly review. Someone opens the ads console, points at a column and says: “our acquisition cost is 95 pesos.” Nobody questions it, because the number looks fine. Three months later the bank account does not match the story that column was telling, and nobody can explain why.

What happened is a vocabulary problem with financial consequences. The column said CPA — cost per action, or per acquisition — and the room heard CAC, customer acquisition cost. The names are so close that the confusion is nearly unavoidable, and yet the two measure different things, come from different sources and support different decisions.

The difference is not academic. CPA is almost always smaller than CAC, sometimes by a lot. Report one believing it is the other and your business looks more efficient than it is — and the decision that follows, whether to raise budget, cut price or open a new category, rests on a false floor.

On a marketplace the confusion gets worse, because the channel hands you CPA effortlessly and CAC almost not at all. This article separates the two, shows the arithmetic that distinguishes them, and proposes a practical way to measure the gap between them in your own business.

what CPA measures

CPA is the cost of an action: a conversion, a concrete event you defined as valuable. In marketplace advertising that action is almost always an order attributed to an ad.

The formula is direct: campaign spend divided by conversions. Spend 9,500 pesos across a set of campaigns, have those campaigns register 100 attributed orders, and your CPA is 95 pesos. Nothing more, nothing less.

Three properties define CPA and explain why it is so useful:

• It is campaign-level, not business-level. Every campaign, ad group and keyword has its own. You can compare them against each other.
• It is immediate. You can read it with two days of data and act the same afternoon. That is why it is the metric you operate with.
• It only counts what the platform sees. The numerator is that platform’s spend; the denominator is the conversions that platform attributes to itself, under its own attribution windows.

CPA is an excellent operational metric. It tells you which campaign to pause, which keyword to kill and which ad deserves a higher bid. The trouble starts when it gets carried into the results meeting as if it described the business.

what CAC measures

CAC is the cost of getting one new customer, and it is a business metric, not a campaign one. Its numerator includes everything you spent acquiring: ad spend across every channel, first-purchase coupons and discounts, fees paid to whoever runs the campaigns, content produced for them. Its denominator counts new people, not orders.

Swapping “action” for “new customer” does two things at once. It raises the numerator, because costs the platform never saw now count. And it lowers the denominator, because orders from people who had already bought no longer qualify. Both push the number the same way: CAC is always greater than or equal to CPA, never smaller.

That is why CAC is not read daily or per campaign. It is read monthly and per channel, and it answers bigger questions: whether the business can absorb the cost of growing, how much budget the margin can carry, whether a new category is worth opening.

Glossary: ACoS is the share of attributed sales that went to advertising; CPA is that same spend expressed as pesos per order →

the arithmetic that separates them

Take a month on Amazon Mexico. The console reports 9,500 pesos of spend and 100 attributed orders. CPA: 95 pesos. That is the number the operator sees.

Now the CAC for the same month. The numerator picks up 1,800 pesos of first-purchase coupons and 4,200 for the freelancer running the campaigns: 15,500 pesos. The denominator drops the orders that were not from new buyers: of the 100 orders, Amazon’s new-to-brand metrics flagged 60 as purchases from someone who had not bought your brand in the previous twelve months. CAC: 15,500 over 60 = 258 pesos.

95 against 258. The same reality, two numbers that differ by almost three times. If that product’s net margin is 190 pesos per unit, CPA says you make 95 pesos per order and CAC says every new customer costs you 68 pesos more than they leave on their first purchase. One reading invites you to raise the budget; the other forces you to ask how often that buyer returns before you do.

The gap between them — here, 2.7x — is itself a metric worth watching. If your CPA stays flat while the gap widens, the same spend is buying more repeat orders and fewer new buyers. No column in the console shows you that.

why the confusion is so easy

Three reasons, and none of them is carelessness.

The first is the name. In the industry, the A in CPA is read as either action or acquisition, and “cost per acquisition” sounds exactly like “customer acquisition cost.” Ad platforms use the term in the action sense; the finance side hears it in the customer sense.

The second is availability. CPA is on screen, current, segmented by campaign, with zero work from you. CAC has to be assembled by hand, crossing third-party invoices with orders from two channels. When one metric is free and the other costs effort, the free one wins.

The third is that on a marketplace the correct denominator barely exists. Amazon offers new-to-brand metrics, which it defines as a purchase from someone who bought no product from your brand in the previous twelve months; they require Brand Registry and report natively in Sponsored Brands and Sponsored Display, not in Sponsored Products, and availability has shifted by country and campaign type — worth confirming in Seller Central and the Amazon Ads console. MercadoLibre publishes no equivalent metric in Product Ads. Without that denominator, most people default to CPA.

what the public measurements say

Time to be blunt: there is no public CPA or CAC benchmark for Mexican marketplace sellers, and none for the gap between them either. What circulates comes from other worlds and should be read that way.

The most-cited CAC benchmarks come from direct-to-consumer stores, in dollars. Shopify published 2021 data for stores with fewer than four employees, ranging from roughly $21 in arts and entertainment to $377 in electronics; the US agency First Page Sage publishes an industry report built from its own portfolio of 80-plus clients between 2020 and 2025, ranging from about $53 in food and beverage to $91 in jewelry. That two serious sources differ fivefold on electronics is not an error: it is proof that each puts different costs in the numerator. They are order-of-magnitude references, from a US market and from owned stores — not targets for MercadoLibre Mexico.

On the CPA side, published benchmarks come from search and social platforms, not marketplaces. WordStream, which publishes an annual Google Ads study, reported an average conversion rate of 7.52% across industries for 2025, with enormous spread between verticals. That is useful for understanding that conversion — and therefore CPA — varies wildly by what you sell, but it does not transfer to Amazon or Meli, where the shopper arrives with purchase intent already formed and conversion rates look nothing alike.

The practical conclusion is the same as with any acquisition metric: outside numbers help you rank categories, not set a target. Your target comes from your margin.

Glossary: real net margin, with commissions, fees, shipping, tax and advertising already deducted →

when to use each one

The rule fits in a sentence: CPA is for operating, CAC is for deciding.

• To pause a campaign, move a bid, kill a keyword or compare two ads: CPA. Fast, granular, needs nothing else.
• To set the quarter’s budget, judge whether a new channel pays for itself, or negotiate with a partner or a bank: CAC. It is the only one that describes what growth actually costs.
• To review the health of the business month over month: both, plus the gap between them.

And one use almost nobody exploits: the gap as an early warning. If CPA falls while CAC rises, either an off-platform cost is growing unchecked — coupons, agency, production — or your advertising is buying fewer and fewer new buyers. Neither is visible from a single metric.

how this reads in iqseller

In the panel, CPA lives naturally on the advertising side, and CAC gets assembled by crossing that spend with the period’s profitability.

The Profitability module contributes the part no ads console has: net margin per SKU with the COGS you loaded, commissions from the Amazon settlement and from MercadoLibre orders, FBA and Full fees, shipping, the VAT and withholding breakdown, and the same period’s advertising. That margin is what decides whether a 95-peso CPA or a 258-peso CAC is healthy; without it, both are just numbers.

Because advertising from both channels lands in the same period and the same Parent → Model → SKU tree, the comparison stops being “Amazon account versus Meli account” and becomes per product family, which is where decisions actually get made. And in Alerts, the thing worth watching is not CPA, which moves daily, but the margin holding it up: when a SKU’s net margin falls, a CPA that was acceptable yesterday becomes a loss without anyone touching the campaign.

the rule that keeps them straight

Keep this distinction and you will not slip again: CPA counts orders, CAC counts people. An order is an event; one person can generate several orders over a year. Any metric whose denominator is orders is a CPA, whatever the column calls it.

And a second rule, for when you present numbers: always say out loud what is in the numerator and what is in the denominator. “Amazon Ads spend over attributed orders” leaves no room for doubt; “our acquisition cost” does. That extra clause is what separates a meeting that decides well from one that decides on the wrong number.