Cost per acquisition calculator
Spend divided by customers is the easy part. Whether that number is survivable depends on your margin — so put it in.
The ceiling nobody calculates before spending
Cost per acquisition only means something next to gross profit per sale. An eighty-five dollar order at forty-five percent margin produces about thirty-eight dollars of gross profit, so a CPA above that loses money on every single sale, no matter how good the campaign looks by any other measure. Scaling a campaign in that state does not fix it, it accelerates it.
That maximum sustainable CPA — shown above once you enter margin — is the single most useful number to know before you set a bid. It is the ceiling. Anything below it earns; anything above it burns.
Two things this deliberately does not assume. Repeat purchases: if customers buy several times, the lifetime value rather than one order can justify a higher CPA, but only if you actually measure the repeat rate rather than hoping for it. And overheads: gross margin sits above your fixed costs, so a campaign breaking even on gross profit is still not paying for the business around it.
Questions
What CPA can I afford?
Up to your gross profit per sale, shown above once you enter margin. Below that you profit on the first order; above it you need genuine repeat purchases to make the maths work.
Is CPA the same as CAC?
Closely related. CPA usually means cost per conversion within a campaign; customer acquisition cost normally includes wider sales and marketing costs and is measured per new customer rather than per order.
Should I use gross or net margin?
Gross margin, which is what this expects. Just remember it excludes overheads — breaking even on gross profit still leaves the rest of the business unpaid.