How to calculate customer acquisition cost
Performance and growth
6 min read
Published: · Updated:
Your ad dashboard says “cost per result: $20”. You divide the month’s ad spend by the new customers who came from ads and get $300. Both numbers are right; they just count different things. Customer acquisition cost (CAC) is the total you spend on marketing and sales in a period, divided by the number of new paying customers in the same period. The formula is one line. The hard part is deciding who counts as a customer and which costs go in.
The numbers below are fictional, picked only to show the arithmetic: a small online sewing course. Don’t read them as an industry average or a target.
Who counts as a customer?
The dashboard’s $20 counts form submissions: $1,200 of ad spend divided by 60 forms. A person who fills in a form is a lead. A person who pays is a customer. Of the 60 forms, 11 people enrolled in the course, so the denominator for CAC is 11.
Cost per lead is a useful number, but it answers a different question: do the ads get people to the form? It doesn’t say whether those people end up enrolling.
Which costs go on top?
Counting only ad spend is like writing down the rent and forgetting the bills. A fuller count includes:
- Ad spend
- The work of whoever prepares the ads and content, or the outside fee
- Time spent on sales calls
- Subscriptions for marketing tools
For the sewing course, one month looks like this: ads $1,200, a freelancer making content $600, tool subscriptions $150, and call time worth $250. Total: $2,200. New students: 11. CAC: $2,200 ÷ 11 = $200.
With ads only, the same month would give about $109. That’s almost half. You may not be able to include every cost; that’s fine, but write down what you included, and use the same method every period. Being able to compare month to month is worth more than a perfect count.
What if spend and sales don't line up?
Money spent this month often doesn’t produce this month’s customers. If someone sees an ad, thinks it over for three weeks, then enrols, there’s a lag. Two fixes: widen the window and look at three months at once, or trace each customer back to where they first came from.
The second one needs measurement. If you have none yet, even a single field on the form, “How did you hear about us?”, is a start. For a proper setup, see GA4 setup step by step.
Why split it by channel?
One total won’t tell you which channel is the expensive one. Here is the same month, with shared costs (tools and call time) left unallocated:
| Channel | Direct spend | New students | Cost per student |
|---|---|---|---|
| Ads | $1,200 | 4 | $300 |
| Organic search and content | $600 | 3 | $200 |
| Word of mouth | $0 | 4 | no direct spend |
Don’t read this as “word of mouth is free”. Those students came from earlier happy students, and those courses had costs too. What the table is good for is raising a question: why are ads the most expensive here? Is the message weak, the landing page, or the call that follows?
Four sign-ups per channel is also thin. The example shows the logic only; in a real account, collect a few months first.
Is the number good or bad?
There is no universal threshold, and we’d rather say so than invent one. Two things help you judge it: is what a customer brings you over their lifetime higher than what it cost to win them, and how long do they stay or do they buy again? A student who enrols in a second course moves the first cost to a very different place.
Both numbers come from your own records. An industry average won’t describe your situation, so compare against your own earlier periods.
The one table to fill in each month
One table is enough to start. Rows are periods; columns are channel, spend, leads, customers and CAC. The gaps you hit while filling it in are information too: if you can’t say where a customer came from, that’s where measurement needs to be set up.
Add one sentence at the end of each period: what did we see, what will we do? Six months on, those lines are worth more than the table.
If the question is how to split a budget between ads and organic search, SEO vs. advertising walks through it.
What decision will this table change?
Before you build any of this, ask which decision the number is for. “Should I raise the ad budget?” and “which channel brings the cheapest customer?” need different tables. Once the question is picked, how many indicators to follow is settled too.
Frequently asked questions
How do you calculate customer acquisition cost?
Divide the total marketing and sales spend in a period by the number of new customers won in the same period. For example, $2,200 spent in a month and 11 new customers gives $200 each. That figure is fictional; use your own records for your own calculation.
Which costs are included in CAC?
Ad spend, the work or fees behind ads and content, time spent on sales conversations, and marketing tool subscriptions. If you can’t gather all of them, write down which ones you counted and keep the same method each period so the numbers stay comparable.
Is cost per lead the same as CAC?
No. Cost per lead counts people who contacted you, whether or not they paid. CAC counts only paying customers. If the two drift far apart, the problem may be in the sales call or the quote stage, not in the ads.
What if I have no data yet?
Start today. Mark earlier periods as “data needed” and begin recording spend, new customers and each customer’s source for the coming month. A single table and a “how did you hear about us” question is enough for a first calculation.
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