Most of those orders are repeat customers you didn’t acquire this period. This works out true CAC (spend divided by new customers only) and checks it against what a first order actually contributes.
Pull these from the same period in Ads Manager and Shopify.
What a single order actually contributes, before ad spend.
First order runs -£8.38 after CAC. At this contribution per order, it takes 1.24 orders from a customer to pay back what it cost to acquire them.
The spreadsheet version, plus the note on why blended CPA flatters retention-heavy accounts.
Also worth a look: the ROAS you actually need to see
One calculator rarely tells the whole story. This is the order that actually works: from margin, to target, to a page that can convert the traffic you send it.