Customer acquisition cost

A company can grow ARR and still be dying. The first number in that verdict is CAC (customer acquisition cost): what it really costs to win one more customer.

If the unit loses money, scaling marketing or hiring more salespeople makes the hole deeper. The math is simple. The traps are in what you put in the numerator and who you put in the denominator.

CAC = (Sales + Marketing spend in period) / New customers in period

Fully loaded means salaries, commissions, benefits, tools (CRM, ad platforms), agencies, events, and the share of marketing content that exists to generate pipeline — not just ad spend.

The big idea

CAC is the fully loaded cost of opening the door, not the ad click that walked through it. Organic customers look free in a paid-only number and still consume product, support, and brand spend.

The analogy of a "cost per door" breaks across time: spend this quarter closes deals next quarter. For a rough operating metric, use the same period for spend and logos and note the lag. For board-quality math, lag CAC by your average sales cycle (for example, divide Q1 S&M by Q2 closed-won if the cycle is about 90 days).

Walking through it

• Blended CAC uses all S&M and all new customers (paid + organic + referrals).
• Paid CAC uses only paid acquisition spend and only customers attributed to paid.

Early PLG companies often show a beautiful paid CAC and a scary blended one once they staff a sales team. Report both. Argue with neither.

The unit of analysis should match how money moves. For B2B SaaS that is usually a customer or account. Marketplaces use an order. Consumer uses a first purchase. Usage businesses use a customer or API key. Same shape; different revenue and COGS lines. See marketplace economics and API economics.

Common mistakes

• Ad spend only in the numerator. Salaries and tools are usually the bulk.
• Calling organic free. Blended CAC is what the business pays.
• Ignoring sales-cycle lag. This quarter's spend closed last quarter's pipeline.
• One blended CAC across SMB and enterprise. You are averaging two businesses.

Check yourself

S&M is $315k, 21 new logos. What is blended CAC?

$15,000.

Why report paid and blended?

Paid looks cheaper when organic is in the denominator of one and not the other. The company paid for both.

Key takeaways

• CAC is fully loaded S&M divided by new customers.
• Track blended and paid separately. Organic is not free at the company level.
• Lag spend by the sales cycle when you need board-quality math.
• Segment by channel and ACV. A blended number hides the segment that does not work.

Further learning

Startup Killer: the Cost of Customer Acquisition (David Skok)In the many thousands of articles advising entrepreneurs on what they have to focus on to build successful startups, much has been written about three key factors: team, product and market, with particular focus on th…For Entrepreneurs

Next: contribution margin.