How to calculate customer acquisition cost (CAC)
CAC is one of the most-quoted numbers in business and one of the most-fudged. Calculate it honestly and it tells you whether growth is building a business or quietly burning cash.
Skip the math — the free roas calculator runs this from your own figures.
Open the free calculator →The basic formula
Customer acquisition cost is the total you spent to win customers over a period, divided by the number of customers you won in that period. Spend $10,000 on sales and marketing in a month, land 50 new customers, and your CAC is $200.
That's the whole formula. The difficulty isn't the division — it's being honest about the numerator.
What actually belongs in the cost
Most people count only ad spend, which flatters the number. True CAC includes everything you spent to acquire customers: ad spend, the salaries of the marketing and sales people, the software they use, agency or freelancer fees, content costs, and sales commissions.
Leave those out and your CAC looks great while the business bleeds. Include them and you get the number your bank balance actually responds to.
Match the time periods
Spend and customers should cover the same window. If there's a lag between when you spend and when the customer signs — common in longer sales cycles — comparing this month's spend to this month's signups can mislead.
For most small businesses a monthly or quarterly view is fine. If your sales cycle is long, line up the spend with the period it actually produced customers in.
CAC means nothing on its own
A $200 CAC is neither good nor bad until you compare it to what a customer is worth. That's why CAC is almost always read next to LTV (lifetime value) as the LTV:CAC ratio, and next to how long the customer takes to pay you back (CAC payback).
A rough industry rule of thumb is that a customer's lifetime value should be around three times their acquisition cost. Below that, you're spending too much to grow; well above it, you may be under-investing in growth.
Turn CAC into a decision
Once you know your real CAC, you can set a maximum you're willing to pay for a customer, hold each channel to it, and cut the ones that blow past it. That single discipline is what separates profitable growth from expensive noise.
The free calculator below works out your CAC, ROAS, and profit-after-margin per channel from your own numbers, so you're comparing channels on the true cost — not just ad spend.
Questions
What's the difference between CAC and CPA?
CPA (cost per acquisition) usually means the cost of a single conversion action inside one channel — a lead, a signup, a trial. CAC is broader: the fully-loaded cost of acquiring a paying customer across all sales and marketing. A low CPA on one ad can still sit inside a high overall CAC once salaries, tools, and sales effort are counted.
Should CAC include the cost of acquiring existing customers again?
No. CAC measures the cost to acquire new customers, so the numerator should be acquisition spend and the denominator new customers only. Money spent retaining or upselling existing customers belongs to retention or expansion metrics, not CAC — mixing them in distorts both numbers.