CAC

Customer acquisition cost, or CAC, is the total sales and marketing spend in a period divided by the number of new customers won in that period. If you spent $30,000 on ads, salaries, software, and agency fees in a month and won 100 new customers, your CAC is $300. It lives in your accounting and customer records, not in Google Ads or Meta Ads Manager, which is why no ad platform shows it for you. The fully loaded version counts every go-to-market dollar. A looser version, sometimes called paid CAC, counts only ad spend, so always ask which one someone means when you hear a number. Investors and finance teams use CAC to judge how efficiently a business grows, and it often appears next to lifetime value in a ratio.

The calculation sounds simple but depends on choices. What counts as new: a first-time buyer, a customer who returned after a year, a free trial that converted? Which costs belong: creative production, a salesperson's pay, the commission to an affiliate? What period matches: for a long sales cycle, this month's spend produced next quarter's customers. Two honest teams can compute very different figures for the same business. The number is also an average. It hides that your cheapest customers may come from referrals and your most expensive from paid campaigns, so a blended CAC does not tell you what the next ad dollar will cost. Payback period, the months needed to earn back the CAC from a customer's gross profit, is a practical companion metric for small businesses with tight cash.

CAC is different from the cost metrics inside ad platforms. Platform cost per acquisition divides ad spend by conversions that platform counted, using its own attribution window, and excludes salaries and tools. Google's help page on Target CPA bidding describes the target as an average cost per conversion, which is a campaign-level concept, not a business-level one. A platform CPA of $40 and a CAC of $140 can both be correct, because they measure different things. That is why CAC is compared against customer lifetime value, not against campaign dashboards, and why it should be reconciled with your bank, not your ad account. Segment it if you can. CAC from referrals, organic search, and paid ads differs widely, and the blended figure hides which sources carry the average.

The common mistakes are mixing definitions and ignoring who counts as new. Dividing ad spend by all orders, including repeat buyers, flatters CAC. Using platform-reported conversions means the denominator may include sales that would have happened anyway, or double-count the same sale that Meta and Google both claim. Another mistake is optimizing campaigns to a low CPA while CAC rises, because the cheap conversions were low quality leads that cost sales time to chase. A third is ignoring time lag, which makes a fast-growing month look cheaper than it is. Be wary of attribution fights. If Google and Meta each claim the same customer, the platforms together report more customers than you actually have, and your own records settle the count. If you only have rough numbers, start rough.

To use CAC, compute it monthly with a written definition and keep that definition fixed. Compare it with gross profit per customer over a realistic horizon, such as the first year: if each customer brings $400 in profit and CAC is $300, you have room; if CAC is $450, you are buying customers at a loss. This week, pull last month's total sales and marketing cost, count new customers from your own records rather than ad platforms, and write the result next to your platform CPA. The gap between the two numbers is the overhead and misattribution your dashboards do not show. Revisit the definition when the business changes, for example when you hire a salesperson, because last year's CAC will no longer compare.