The basic formula

Customer acquisition cost, or CAC, is the average amount you spend to win one new paying customer. The formula is short: total acquisition costs for a period, divided by the number of new customers you gained in that same period.

If you spent $6,000 on ads in March and gained 120 new customers, a quick CAC is $50. The trouble is that $6,000 was not all you spent to get those customers. The honest number almost always sits higher.

What belongs in the cost

A fully loaded CAC includes every cost you would not have paid if you stopped trying to win new customers. Most small businesses should count:

  • Ad spend on every platform, including the ones you rarely check.
  • Agency, freelancer and consultant fees for marketing and sales.
  • Software used mainly for acquisition: ad tools, landing-page builders, email tools for new leads.
  • Staff time: the share of salaries or your own hours spent on marketing and selling.
  • First-order discounts, free trials, free shipping offers and referral bonuses.
  • Creative costs such as photos, video and design.
The same 120 new customers, as more real costs are counted
  • Ad spend only$50
  • + agency & software$65
  • + staff time$82
  • + first-order discounts$90

A calculation, not survey data: $6,000 ads, $1,800 agency and software, $2,040 staff time and $960 discounts, divided by 120 new customers.

Source: Worked example

Why staff time matters more than people think

People are a large part of what marketing costs. Gartner's 2026 marketing survey found that labor's share of the total marketing budget rose to 24.5% in 2026, up from 21.9% in 2025. Gartner's 2026 CMO Spend Survey, drawn from the same 401 marketing leaders, put total marketing budgets at 7.8% of company revenue. The respondents were mostly large companies, but the lesson carries over: leave labor out and you leave out roughly a quarter of the bill.

For an owner-run business, your own time counts. If you spend ten hours a week on ads and sales calls, put a fair hourly value on it. You might choose not to pay yourself today, but if you ever hire someone to do that work, your CAC will jump overnight.

The chart on this page shows how the same 120 customers look as costs are added. Ad spend alone gives $50. Adding agency and software fees takes it to $65. Adding staff time takes it to $82. Adding first-order discounts lands at $90, almost double the first figure.

Count real new customers, not conversions

The bottom half of the formula needs as much care as the top. Ad platforms report conversions, which can include repeat buyers, sales also claimed by another platform, and people who never actually paid. Read more in why ad platforms claim more sales than you made.

For CAC, count first-time paying customers from your own records: Stripe, your store, or your CRM, the system where you track customers and deals. Remove refunds and test orders. If one person buys three times, that is one new customer.

It also helps to keep two versions. Paid CAC divides paid marketing costs by customers who came through paid channels, which helps you judge your ads. Blended CAC divides all acquisition costs by all new customers, including those from word of mouth, which shows the true average cost of growth.

What to do with the number

CAC means little on its own. Its job is to be compared with what a customer is worth. A $90 CAC is a problem if the average customer brings in $60 of gross profit over their lifetime, and a bargain if they bring in $400. Our guides to customer lifetime value and the LTV to CAC ratio show how to make that comparison.

Look at the trend too. A CAC that climbs month after month while spend stays flat often means an audience is tiring of your ads, or a channel is getting more crowded and expensive.

Matrix ROI lets you upload exports from any ad platform beside your Stripe payments, so new-customer counts come from money you actually received. It was created by Smith App Studio for owners who want that comparison in one place.