Software Growth

CAC (Customer acquisition cost)

CAC is the average sales and marketing cost of winning one new paying customer. It tells you how much you can afford to spend to grow.

Customer acquisition cost is what you spend, on average, to turn a stranger into a paying customer. For a SaaS founder it is the number that decides which channels you can afford, how fast you can grow without outside money, and whether the business works at all.

David Skok makes the point that entrepreneurs usually underestimate this number, assuming customers will line up for a good product. In practice the cost of finding, convincing and onboarding each customer is often the biggest line in the budget.

How to calculate CAC

Example: last month you spent $6,000 on ads, $2,500 on a freelance writer, $1,500 on tools, and $2,000 of your own time valued at a contractor rate, for $12,000 in total. You won 40 new paying customers.

On its own $300 means nothing. It only makes sense next to what a customer pays you and how long they stay.

What to include

Count every cost tied to winning customers, not just ad spend. That means salaries or contractor fees for sales and marketing, commissions, software, content, events and onboarding help for new accounts. If you leave your own time out, your CAC looks better than it is.

  • Match the period: if deals take 60 days to close, compare spend from two months ago with customers won now.
  • Count only new customers, not upgrades or reactivations.
  • Exclude free users who never paid, unless you are measuring cost per signup.

The a16z guide separates paid CAC (only customers from paid marketing) from blended CAC (all channels, organic included). Blended is flattering because word of mouth and SEO dilute it. Paid CAC tells you whether the next dollar of advertising will pay off.

What good looks like

A low CAC is not automatically good. Judge it against customer lifetime value and the CAC payback period. Skok says the best SaaS businesses have an LTV to CAC ratio above 3, and that a healthy business recovers CAC in roughly 5 to 7 months, with 12 months being the line past which profitability is anemic. See LTV:CAC ratio for the full picture.

CAC for bootstrapped products

Without investor cash, you cannot wait 18 months to get your money back. A product at $50 per month with a $300 CAC is fine if customers stay a year or more, but it will strain your bank account in the meantime because you pay up front and collect slowly. Cheap channels such as content, SEO, partnerships and founder-led sales usually beat paid ads for small teams, even when they look slow.

Common mistakes

  • Using only ad spend and ignoring salaries and tools.
  • Averaging across segments that behave very differently, like self-serve and sales-assisted customers.
  • Calculating CAC in a month with unusually low spend or a one-off launch spike.
  • Never checking it against margin: a $300 CAC on a product with 40% gross margin is much worse than on one with 80%.

Sources

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