Agree on metric definitions, cost categories, time windows and decision thresholds together. The CMO explains the buyer and channel assumptions; the CFO tests cash, margin and risk. A shared model prevents marketing from reporting efficient leads while finance sees poor customer economics.
Put one definition beside each metric
Write what is included in customer-acquisition cost: media, people, tools, agencies and sales effort, plus the period in which costs and customers are counted. A blended number is useful for some board questions but may hide channel decisions. The CAC definitions guide shows why two honest teams can report different figures.
Connect buyer timing to cash timing
Marketing may generate an enterprise opportunity today that cannot close for months. Finance needs to know the expected time to feedback, cash available for tests and what early signals justify continuing. Do not treat an unproven pipeline value as booked revenue. The CMO should explain the buyer journey; the CFO should test downside exposure.
Set gates before committing spend
For each major experiment, record the hypothesis, cost cap, leading signal, review date and what happens if the signal fails. This protects learning without turning every small change into a finance meeting. Use scenario ranges rather than a precise forecast built on tiny samples. If the result is ambiguous, decide whether to extend the test or shift the investment.
A bounded example
A hypothetical startup sees paid search generate cheap demos. Finance sees a high fully loaded acquisition cost after sales effort and low conversion. The shared review separates lead-quality issues from a long sales cycle and identifies whether the next dollar belongs in traffic, conversion or sales enablement. That is a more useful conversation than arguing over whose dashboard is correct.
A shared cost and cohort worksheet
Choose one acquisition period and trace spend through to customers from that cohort. List paid media, agency and contractor fees, internal people costs, tools and sales effort separately before choosing what to include in a given CAC view. Label first-order revenue, gross margin and future expected value separately. A forecast is not observed cash. For a long buying cycle, note when the cohort can be judged fairly.
The CMO and CFO should review three cases: base, upside and downside. What happens if lead quality is lower than expected, conversion takes longer or a channel requires more production? Decide how much the company can risk before the first reliable feedback point. An agreed test budget allows learning; an agreed stop rule prevents a weak test from expanding because its early dashboard looks attractive. The shared model also makes board reporting more honest: a channel may have promising leading evidence while its full economics remain unproven.
Frequently asked questions
Should the CFO approve every marketing experiment?
Usually the CFO should agree on the budget and risk boundaries; routine tests can then run within delegated limits. The exact thresholds depend on company policy.
Why do CAC reports disagree?
Teams may include different costs, periods and customer counts. Reconcile the formula and cohort before comparing channels or judging performance.
Do marketing and finance disagree about whether growth is working?
Bring the current CAC calculation, channel spend and sales-cycle assumptions. We can make the decision model consistent enough to guide budget choices.
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