Cost per order against CAC: what's the difference?

Updated 16 October 2026 · 4 min read

Cost per order, CAC and CPA all sound like the same thing: what it costs to get a sale. They aren't, and mixing them up leads to bad calls, such as cutting ads that are working or celebrating a number that is propped up by loyal customers. Here is what each one means and when to use it.

The short answer: cost per order is total ad spend divided by every order your store took. CAC (customer acquisition cost) is marketing spend divided by new customers only. Because returning customers order too, CAC is never lower than cost per order, and usually well above it. Judge cost per order against what an order earns you, and CAC against what a customer is worth over time.

Three numbers that sound alike

Cost per order = total ad spend ÷ all orders. Every order counts, new customer or not, whichever channel it came from.
CAC = marketing spend ÷ new customers. Only first time buyers count.
CPA (cost per acquisition, or cost per purchase) = one platform's spend ÷ the purchases that platform claims. It is the platform's own view, with the same overlaps as platform ROAS.

A worked example

In one month a store:

spends £6,000 on ads across Meta, Google and TikTok
takes 400 orders in Shopify
of which 160 came from first time customers and 240 from people who had bought before

Cost per order = £6,000 ÷ 400 = £15.
CAC = £6,000 ÷ 160 = £37.50.

Meanwhile Meta might report a CPA of £20 on its own spend, and Google £12 on its own. Four different figures, all correct, all answering different questions.

Why CAC is higher

Cost per order spreads your ad spend across every order, including the ones from returning customers who came back through an email or straight to your site. CAC puts all of that spend on new customers alone. The more loyal your customers, the wider the gap.

That gap can hide a problem. If returning customers are growing while new ones dry up, cost per order can look fine, even improve, while CAC quietly climbs. Ads are meant to find new people, so keep an eye on both.

Some brands also work out a fully loaded CAC, which adds agency fees, creative production and discounts given to first orders on top of ad spend. It is the truest cost of a new customer, but needs more bookkeeping.

What to judge each one against

Cost per order against profit per order. Take your average order value, then take off product, delivery and payment costs. If an average order leaves £24 before ads and your cost per order is £15, each order clears £9. If cost per order creeps above £24, the average order loses money.
CAC against customer value. A new customer is worth their first order's profit plus whatever they buy later. If the first order leaves £24 and customers typically come back for another £30 of profit within a year, you can afford a CAC above £24 and still win, as long as the repeat orders really happen. Work this out from your own repeat rate, not an industry average.
CPA against other ads on the same platform. It is the right tool for choosing which ads to keep, not for judging the business.

Working out CAC from Shopify

You need the number of new customers for the same dates as your spend. Shopify's own analytics reports can split sales between first time and returning customers. Take the count of first time customers for the month and divide your total ad spend by it.

Use the same dates and the same spend figure each time, and decide once whether CAC includes only ad spend or the fully loaded costs. A CAC that changes definition from month to month can't be compared.

Why That Other Dashboard shows cost per order

That Other Dashboard shows cost per order: total ad spend across your connected platforms divided by your Shopify orders. It counts every order, not just the ones a platform claims, so it can't be inflated by overlapping attribution.

It doesn't show CAC because working out new customers means reading who each customer is, and That Other Dashboard deliberately keeps no customer details: no names, emails or customer IDs. For CAC, use Shopify's customer reports alongside it as above. Each ad's own cost per purchase sits in the ads table, where it is useful for comparing one ad with another.

Common questions

Is CPA the same as CAC?

No. CPA is what one ad platform says each purchase it claims cost, including purchases from returning customers. CAC is your total marketing spend divided by genuinely new customers, counted in your own store.

What is a good cost per order?

One comfortably below what an average order leaves you after product, delivery and payment costs. A £15 cost per order is fine on an £80 order with good margins and ruinous on a £25 one.

Should CAC include email and SMS costs?

It can, if you are working out a fully loaded CAC. Most brands start with paid ad spend only, because that is where most of the money to find new customers goes. Pick one definition and keep it.