CPA vs CAC
CPA is a channel metric; CAC is a company metric. CPA divides paid-media spend by paid conversions. CAC divides all sales and marketing cost, salaries, tools, agencies, creative, by all new customers. CAC is always higher, and the gap is your overhead per customer.
The split
What CAC counts that CPA ignores
| Cost line | In CPA? | In CAC? |
|---|---|---|
| Media spend | Yes | Yes |
| Agency and freelancer fees | Rarely | Yes |
| Creative production | Rarely | Yes |
| Marketing and sales salaries | No | Yes |
| Martech and data tools | No | Yes |
| Organic-acquired customers in the denominator | No | Yes |
Worked
The reconciliation
A month: $50,000 media spend, 800 platform-attributed conversions, so channel CPA is $62.50. Finance counts $130,000 of total sales-and-marketing cost and 1,000 new customers from all sources, so CAC is $130. Both are right. The board deck takes CAC, because payback and LTV ratios are company economics. The channel review takes CPA, because a media buyer cannot optimize salaries. Trouble starts when one number is used for the other job: a platform CPA in a board deck understates acquisition cost by half in this example.
Reconcile
Making platform CPA and finance CAC agree
- Deduplicate the denominator: platforms each claim conversions; finance counts each customer once. Expect platform-summed conversions to exceed real customers.
- Time-shift: CAC books cost in the month incurred; conversions land later. Compare quarter-scale windows.
- Start from blended CPA: total paid spend over deduplicated paid customers is the halfway house both teams can agree on.
Ceiling math: break-even CPA. SaaS framing: SaaS benchmarks. Definitions: the formula page.