What is Customer Acquisition Cost (CAC)?

Customer Acquisition Cost (CAC) is the average amount you spend to turn a stranger into a paying customer. You calculate it by adding up everything you spent on sales and marketing over a period — ad spend, salaries, software, agency fees, content — and dividing by the number of new customers you won in that same period.

CAC is one of the two numbers that decide whether a business is actually viable. On its own it means little; it only becomes useful when you compare it to how much a customer is worth to you over time (see LTV) and how long it takes to earn the money back (see payback period).

How to calculate CAC

The basic formula is total sales and marketing spend divided by the number of new customers acquired. If you spent $10,000 last month and signed 50 new customers, your CAC is $200.

The honest version includes the fully loaded cost: the salaries of the people doing sales and marketing, the tools they use, and any commissions or referral payouts. Founders who only count ad spend almost always understate CAC by a wide margin and then wonder why the bank account doesn't match the spreadsheet.

• Blended CAC: all new customers divided into total spend — easy, but hides which channels work.
• Paid CAC: only customers from paid channels divided by paid spend — the number that tells you if ads are sustainable.
• Always pick a time window that accounts for your sales cycle; spend in March may not convert until May.

Why CAC matters when validating an idea

Before you build, a rough CAC estimate tells you whether a business model can ever work. If realistic acquisition costs are higher than what a customer will ever pay you, no amount of product polish will save it. Estimating CAC early — even from competitor ad costs or industry benchmarks — is one of the fastest ways to kill a bad idea cheaply.