Glossary · Unit economics
CAC (Customer Acquisition Cost)
The fully loaded cost to win one customer: acquisition spend divided by new customers. Understated whenever it leaves out creative, tools, onboarding and team time, which is most of the time.
What CAC means
CAC, customer acquisition cost, is what it costs a business to win one new customer: everything spent on acquisition in a period divided by the number of new customers that period produced. It is the denominator of almost every growth decision, from the payback period a board signs off to the budget a channel is allowed to keep.
The arithmetic is simple; the inputs are not. Most reported CAC divides media spend alone by new customers, and leaves out the creative, the tools, the agency fees, the sales and onboarding time and the incentives that the same customers also cost. A CAC built that way is not wrong so much as partial, and every ratio built on top of it inherits the gap.
The CAC formula and a worked example
The formula and an illustration; the corpus line is the audited figure behind it.
CAC = total acquisition spend ÷ new customers
Worked example Illustration, not a client figure
$90,000 of media for 300 new customers reads $300. Add the $30,000 of creative, tools and team time the deck left out and the true CAC is $400.
Why CAC matters in an audit
In an audit, the first job is to load CAC fully. We rebuild it from the ledger: media from the invoices rather than the platform dashboards, then the agency and tooling costs, the creative production, the share of sales and onboarding time that belongs to new customers, and any sign up bonus or first order discount. The fully loaded figure is regularly well above the one in the deck, and the gap is the first finding.
The second job is to split it. One blended CAC across every channel and segment is an average, and averages hide the customers who cost far more than they will ever return. Split by channel, by cohort and by segment, CAC often shows one source of customers that looks cheap at sign up and expensive by month six, because those customers convert at a lower rate, churn faster or never activate.
A CAC is only good or bad next to what the customer earns back, which is why the audit reads it beside contribution margin, payback period and LTV:CAC rather than against an industry average. Across the 74 audits, 22% of SMB marketing spend was wasted paid spend, and every dollar of it sits inside a CAC somewhere.
CAC in the audited cases
Published cases where the cost of winning a customer, loaded fully or split by source, was the finding, each with the audited annual figure.
- Marketplace
CAC looked fine, until we split it by cohort
+$82k a year, findings in 7 days.
Read the case → - Fintech
CAC payback was twice what the board believed
+$57k a year, findings in 6 days.
Read the case → - B2B SaaS
The cheapest leads were the most expensive customers
$68k a year, findings in 6 days.
Read the case → - Services
Lead spend ignored close rate by source
+$47k a year, findings in 5 days.
Read the case → - Fintech
Incentive spend acquired users who never funded
−$96k a year, findings in 7 days.
Read the case → - Fintech
Acquisition ignored default rate by channel
+$88k a year, findings in 7 days.
Read the case → - Marketplace
Buyer subsidies outran the repeat GMV they were meant to unlock
+$66k a year, findings in 7 days.
Read the case → - Pharma
Patient acquisition spend ran above what reimbursement paid
−$71k a year, findings in 7 days.
Read the case →
Questions about CAC
What is CAC?
CAC, customer acquisition cost, is the total cost of winning new customers in a period divided by the number of new customers won. A fully loaded CAC counts media, creative, tools, agency fees, sales and onboarding time and sign up incentives, not media alone.
How do you calculate CAC?
Add up every acquisition cost for the period and divide by the new customers that period produced. $90,000 of media for 300 new customers reads $300; add the $30,000 of creative, tools and team time the media figure left out and the fully loaded CAC is $400. Calculate it by channel and by cohort as well as in total.
What is a good CAC?
There is no good CAC on its own, only a CAC that the customer repays. Read it beside contribution margin per customer: if a customer contributes $25 a month, a $400 CAC takes 16 months to pay back, and whether that is acceptable depends on how long customers stay. Read the payback period page →
Know the term. Now measure it in your own numbers.
CAC, measured against your own accounts in 5 to 7 working days. $10k to $50k of findings, or your money back.
Fixed fee. No retainer. NDA first.
Go deeper
CAC and the wider audit evidence
- All 14 termsThe full glossary: every term with a formula and a worked example.→
- All 74 findingsRanked by annual value, $58k median, each one a real case.→
- The benchmarkWhere 74 SMB marketing budgets leaked, by share of spend and by industry.→
- Margin leaksThe five leak patterns in depth: what each one is and how an audit finds it.→
- Marketing audit checklistThirty checks across paid media, attribution, pricing, retention and reporting.→
- What an audit costsThe 2026 market ranges with sources, against the fixed fee tiers.→