CAC (Customer Acquisition Cost)

What it costs you, fully loaded, to acquire one paying customer.

When to use this

You're deciding how much to spend on growth, comparing channels, or building a payback model. CAC is also the denominator in LTV:CAC, the single best one-number test of whether your acquisition is sustainable.

When NOT to use this

You're so early that 80% of your customers came from your founder's network. CAC math assumes the spend caused the acquisitions. Pre-traction, it doesn't.

Inputs

• Total acquisition spend: Paid media + content production + sales salaries + sales tooling + a fair share of marketing salaries. Fully loaded, not just ad spend.
• New paying customers acquired: New logos who paid you in the period. Exclude trials. Exclude expansion from existing accounts.
• Time window: A quarter is the sweet spot. Monthly is noisy. Annual hides channel shifts.

The math

CAC = total acquisition spend / new customers acquired

It looks trivial. The fight is over the numerator. "Did the content team's salary count? Did the AE who closed an inbound lead count? Did the free tier's hosting cost count?" Answer yes to all three and your CAC doubles overnight. That's the right answer.

A worked example

A B2C app spent $80,000 on growth in Q1 (paid social, content production, sales tools, a fair share of marketing salaries) and got 1,000 new paying users.

Blended CAC = $80,000 / 1,000 = $80

Now break it down by channel:

The blended number ($80) hides that referral is your cheapest channel and paid social is barely worse than content. If paid social rises to $120 next quarter (it will -- channels saturate), the blended number drifts up slowly and you miss the signal. The channel-level number rings the alarm immediately.

How pmtoolkit does it differently

Channel CAC isn't averaged into one number. You see paid vs organic vs referral side by side and can watch each channel's curve over time. The point is to catch saturation before the blended CAC moves enough to alert anyone. By the time paid social goes from $80 to $130 blended, you've been wasting two quarters of budget.

We also separate new-business CAC from expansion CAC. They're different problems with different math, and rolling them together is how companies convince themselves their CAC is improving when really they're just charging existing customers more.

Common mistakes

• Including organic customers in the denominator. If 30% of your sign-ups never saw an ad, dividing total spend by total customers makes paid acquisition look cheaper than it is.
• Ignoring sales salaries. Especially fatal for B2B. A $150K AE who closes 50 deals adds $3,000 to each deal's CAC. Leave them out and your unit economics are fiction.
• Not separating new vs expansion CAC. Expansion is cheap. New logos are expensive. Reporting one number hides which engine is actually working.
• Using last-click attribution instead of channel-level spend. Last-click tells you which channel got credit, not which channel caused the acquisition. For CAC, you want the latter.

Benchmark

LTV:CAC > 3 is healthy. 1 to 3 is marginal. Under 1 is unsustainable. (Illustrative. Real targets depend on payback period and growth stage -- a 2:1 ratio with 6-month payback can be fine; a 4:1 with 30-month payback can sink you.)

Try it

• Live calculator
• MCP tool: pm_calculate_cac
• Related: LTV
• Related: Unit Economics