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F9-04·F9 — Marketing Finance

CAC, Payback, and the Performance Marketing Illusion

The productive tension

CAC as the only honest growth metricandCAC as a systematic illusion that borrows credit from brand investment

The synthesis

CAC is simultaneously the cleanest marginal cost metric in marketing and the most misleading total budgeting framework. It measures the cost of the last customer acquired through trackable channels, which is real. It does not measure the brand-built demand that converts through branded search, direct traffic, and word of mouth, which is also real. Performance marketing reports CAC efficiency that is largely borrowed from brand investment. The evidence-based marketer uses CAC within its natural domain — the marginal optimisation of paid acquisition channels — and never lets it set the total marketing budget.

Learning objectives

  • Define CAC, blended CAC, paid CAC, and payback period and compute them correctly
  • Distinguish attribution from incrementality and explain why the gap matters financially
  • Describe how branded search and direct traffic launder brand investment into performance metrics
  • Analyse the Airbnb 2020 performance-marketing pause as a natural experiment
  • Apply CAC at the marginal level without letting it govern total marketing spend

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