CAC meaning: what customer acquisition cost is and how to calculate it

CAC stands for customer acquisition cost: the average amount a business spends on sales and marketing to win one new paying customer. You calculate it by dividing everything you spent on acquiring customers in a period by the number of new customers that spend produced.

In marketing, CAC is the number that tells you whether growth is affordable. On its own it says little; next to what a customer is worth, it says whether each new customer makes or loses money.

The CAC formula

CAC = (sales spend + marketing spend in the period)
      / new paying customers acquired in the period

Paid CAC = paid media spend
           / new paying customers attributed to paid channels

What goes into spend decides which CAC you have:

• Fully loaded (blended) CAC: ad spend, marketing and sales salaries, commissions, agencies, events, content, and the tools those teams use.
• Paid CAC: media spend only, divided by customers attributed to paid channels. Useful for comparing channels, flattering if you quote it as your CAC.

A worked CAC example

In the third quarter a B2B software company spent:

It gained 150 new paying customers, 60 of them attributed to ads.

Blended CAC = 75,000 / 150 = $500
Paid CAC    = 18,000 / 60  = $300

Both numbers are correct. The $300 paid CAC is what the ads cost per customer they brought in; the $500 blended CAC is what a customer really costs the company once people and tools are counted. If customers pay $40 a month at 80% gross margin, the blended figure takes about 16 months to earn back ($500 / $32), and the paid figure about 9.

CAC vs CPA

Ad platforms report CPA, cost per acquisition, where an acquisition is whatever conversion you set up: a lead, a sign-up, a demo request, a purchase. If 1,000 trial sign-ups cost $18,000, CPA is $18. If 60 of those trials become paying customers, paid CAC is $300. CPA is the right number for tuning campaigns. CAC is the right number for deciding how much you can afford to spend.

Common CAC mistakes

• Counting only ad spend. Salaries are usually the larger part of acquisition cost for B2B companies.
• Dividing by leads, sign-ups or trials. CAC is per paying customer.
• Mismatching the timing. If a typical deal takes two months to close, this month's customers came from spend two months ago. Use a lag or a longer window, such as a quarter.
• Including costs that serve existing customers. Account management and customer success spending on renewals and upsell belong to retention, not acquisition.
• Averaging channels together and stopping there. A blended $500 can hide one channel at $200 and another at $1,400.
• Counting free users as acquired customers. Only those who pay count, at the moment they first pay.

Related metrics

• LTV to CAC ratio: what a customer is worth against what they cost.
• CAC payback period: months of gross profit needed to earn back CAC.
• SaaS magic number: the same idea at company level, in new ARR per dollar of sales and marketing.
• ARPU: the revenue side you compare CAC with.

Get the inputs automatically every week

No single tool knows your CAC, because spend and customers live in different systems. Three skills cover the inputs:

• Google Ads CPA by campaign posts last week's cost per conversion for every campaign each Tuesday, the paid side.
• QuickBooks expenses by category shows month-to-date spend by expense account every weekday, so advertising, payroll and software appear as your chart of accounts names them.
• Stripe new and canceled subscriptions lists each weekday which subscriptions started, your count of new paying customers.

Give your agent the three results and the CAC definition you chose, and have it post blended and paid CAC on one card each month so the trend stays visible.