CAC vs CPA

CPA divides ad spend by every conversion, while CAC divides it by new customers only, so CPA looks cheaper whenever returning customers buy too.

By Berend Vrakking, founder of Product Metrics. Updated 7 October 2026.

Formula

CPA = ad spend ÷ conversions · CAC = ad spend ÷ new customers

Same spend, a different count. New customers are part of the conversions, so with one order per customer CAC is never lower than CPA. New customer acquisition cost (nCAC) is CAC held strictly to customers who have not bought before.

Example

One month, 100 orders, 60 from new customers
Step	Value
Ad spend	€5,000.00
Conversions (orders)	100
New customers among those orders	60
CPA (€5,000.00 ÷ 100)	€50.00
CAC (€5,000.00 ÷ 60)	€83.33

One invoice, two prices: €50.00 per order, €83.33 per new customer. The 40 returning customers are doing CPA a €33.33 favour. Illustrative data.

For one product, and for an account

Products differ in who buys them. A product your regulars keep reordering has a low CPA and a high CAC; a product that pulls in strangers can show a higher CPA and a lower CAC. Blend them into one account CPA and you can no longer see which products win new customers.

Use CPA to judge a sale against the profit it earns. Use CAC when the question is growth, and set it against first-order profit and repeat purchases. With Full Signal Tracking, new customers get their own conversion action in Google Ads, and Product Metrics shows nCAC per product and as an account average.

Common mistake

Putting CPA in the monthly report as the cost of a new customer. Your regulars are in that count, so winning a stranger costs more than the report says.

Questions

Is CAC the same as CPA?

No. Both start from the same ad spend, but CAC ignores orders from people who have bought before. The two only match in a period where every conversion came from a new customer.

Why is my CAC higher than my CPA?

Because returning customers count towards CPA and not towards CAC. The more of your orders come from regulars, the wider the gap: in the example above, 40 repeat orders out of 100 open a gap of €33.33.

What is the difference between CAC and ROAS?

CAC is the cost of one new customer. ROAS is the revenue each euro of ad spend brought back, from new and returning customers alike. A strong ROAS can rest on returning customers while new customers stay expensive.

Keep reading

Customer acquisition cost (CAC)The formula and what a new customer has to pay back.
Cost per acquisition (CPA)Cost per conversion, counting every sale.
Repeat purchase rateHow many customers come back, which sets the gap between CPA and CAC.
Customer acquisition cost for ecommerceThe formula, nCAC and what you can pay for a new customer.
LTV:CAC ratio for ecommerceCompare what a customer brings with what they cost.
Full Signal TrackingNew-customer and profit conversions sent to Google Ads.