Marketing & acquisition
CAC vs CPA: What's the Difference?
CAC (customer acquisition cost) connects acquisition costs to the number of new customers acquired. CPA (cost per acquisition) divides campaign spend by the acquisitions that campaign produced, where an acquisition is whatever conversion event your business counts — a first purchase, a sign-up, a lead. When the acquisition you count is a new paying customer, CPA and CAC can land close together. Often it is something else, so CAC vs CPA — or CPA vs CAC — is really a question of what the denominator counts and what cost scope sits above it.
Formulas and denominators
CAC = Customer acquisition spend ÷ New customers acquired CPA = Total campaign spend ÷ Acquisitions
CAC's denominator is new customers — people or accounts who became paying customers during the period.
CPA's denominator is acquisitions: the conversion events credited to the campaign in the same period. What counts as an acquisition is your definition — it might be a first purchase, but it might equally be a free-trial sign-up or a qualified lead. The cost side is the campaign spend you enter, over the same period.
Worked example: CAC
A business spends $18,000 on acquisition in a quarter and gains 120 new customers in the same quarter. CAC = $18,000 ÷ 120 = $150.00 per new customer.
Worked example: CPA with a defined acquisition
A campaign spends $3,000 in a month and is credited with 400 free-trial sign-ups in that month. If the business counts a trial sign-up as its acquisition, CPA = $3,000 ÷ 400 = $7.50 per acquisition.
If 60 of those trials later become paying customers, the cost per new customer from that campaign is $3,000 ÷ 60 = $50.00. Both numbers are correct; they just count different things. Comparing the $7.50 CPA with a $150 CAC would be meaningless.
Side by side
| CAC | CPA | |
|---|---|---|
| Denominator | New customers | Acquisitions (the conversion event you count) |
| Typical scope | A period, across one or more channels | A campaign, over the same period |
| Answers | What does a new customer cost us? | What did each acquisition cost in this campaign? |
| Links to LTV? | Directly (LTV:CAC) | Only if the acquisition counted is a new customer |
Ways to scope CAC
The cost side of CAC can be defined in several ways. Each is a legitimate analytical approach; none is correct for every situation. What matters is labelling the version you use and keeping it consistent.
- Paid-media-only CAC: ad spend divided by new customers.
- Fully loaded CAC: ad spend plus sales and marketing salaries, tools, agencies and other acquisition costs.
- Channel-level CAC: the cost and new customers attributed to one channel.
- Blended CAC: all included acquisition costs divided by all new customers, regardless of channel.
Match the period and the scope
Spend and customers should come from the same period. Dividing a quarter's $18,000 of spend by one month's 40 customers gives $450.00 instead of $150.00.
Cost scope and customer scope should also match: channel spend with that channel's customers, total spend with total new customers. Mixing them makes CAC look better or worse than it is.
When each metric is useful
- CPA: judging a specific campaign against the acquisitions it produced, and comparing campaigns that use the same acquisition definition.
- CAC: understanding what growth costs at the business or channel level, and comparing that cost with what customers are worth.
CAC, LTV and LTV:CAC
Customer lifetime value (LTV) estimates the revenue a customer brings over their relationship with you. Dividing LTV by CAC shows how many times over that expected revenue covers the cost of acquiring the customer. BizFormula's LTV is revenue-based, so a ratio above 1 does not by itself mean the customer is profitable — product and service costs still have to come out of that revenue.
Common mistakes and edge cases
- Treating CAC and CPA as interchangeable when the acquisition counted in CPA is not a new customer.
- Comparing a paid-media-only CAC with a fully loaded one.
- Counting returning customers as new customers.
- Zero new customers: CAC cannot be calculated with a zero denominator, and BizFormula's CAC Calculator asks for at least one new customer.
- Relying on universal "good CAC" or "good CPA" figures. Useful targets depend on your own margins, pricing and customer value.