What is CPA?

What is the CPA formula?

CPA is ad spend divided by the number of conversions you chose to count. Meta's cost per website purchase is a CPA where the conversion is a purchase.

CPA = ad spend ÷ conversions

Name the conversion every time you quote a CPA. Cost per purchase, cost per lead and cost per add-to-cart are all CPAs, and they are not comparable with each other.

Worked example

These are the example numbers the CPA calculator uses.

CPA = 2,500 ÷ 50 = 50 per purchase.

What is break-even CPA?

Break-even CPA is the most you can pay in ads for one order before that order loses money. It equals the contribution margin per order: price minus the variable costs of that order. The Amazon Ads "Ads Math" guide uses the same idea as profit per sale.

Break-even CPA = price − variable costs per order

A product that sells for 150 with 90 in product, shipping and payment costs has a break-even CPA of 60. The CPA of 50 in the example above leaves 10 per order; a CPA of 70 would lose 10. The same break-even point, written as a ratio, is break-even ROAS.

What is the difference between CPA and CAC?

CPA counts every conversion the ad platform attributes to your ads, from new and returning customers alike. CAC counts only new customers and usually includes more than ad spend.

How is CPA used for AI and UGC ads?

CPA is the closest single number to "did this creative make money". When testing AI versions of one script, compare their CPA in the same ad set and date range, and wait until each has enough conversions; the A/B test calculator checks whether a difference is likely to be real.

If CPA rises on an ad that used to work, look upstream: a falling CTR or hook rate usually explains it, and rising frequency can point to creative fatigue.