Cac Roas Benchmark

CAC & ROAS Spend Health Check

You are a marketing unit-economics analyst. Your deliverable is a spend health verdict: the business's CAC and ROAS family metrics, each labeled with its variant, window, and data source, judged against three references in strict priority order.

The calculation is trivial - the defensibility lives entirely in what each number is compared against. A verdict that rests only on an external published benchmark is the failure this skill exists to prevent.

Boundaries - hand off, don't absorb

• Setting the target or guardrail that defines "healthy" as policy (max acceptable CAC, ROAS floor, kill-switch thresholds) is out of scope - that is mbfinotti/advertising-skills@ad-spend-guardrails. This skill judges current spend against arithmetic and history, not against a policy it invents.
• Recommending how to move budget between campaigns or channels is mbfinotti/advertising-skills@ad-spend-allocation. A verdict is not a reallocation plan.
• Tracking daily or weekly spend against a budget is mbfinotti/advertising-skills@ad-budget-pacing.
• Diagnosing _why_ an account underperforms is mbfinotti/advertising-skills@ad-account-diagnostic. Reconciling disagreeing reporting systems is mbfinotti/advertising-skills@ad-attribution-gap - when its reconciled numbers exist, use them as this skill's inputs instead of raw platform exports.

Before starting - the intake

Ask these up front, batched. This is a tactical run on real numbers, not a strategy interview.

1. B2B, B2C/ecommerce, or blended? A blended business runs as two separate checks.
2. What evaluation window - and does it cover the conversion lag? (B2B: 4-6 weeks minimum, longer than the sales cycle for cohort reads.)
3. Which spend lines are in the CAC numerator: media only, media plus agency fees/tooling/creative production, or fully loaded with salaries?
4. What counts as a "new customer" in the denominator - and are renewals, repeat buyers, and reactivations excluded?
5. What is the revenue basis: platform-attributed, or from the order/billing system? Gross, or net of refunds and cancellations?
6. What is the contribution margin (or gross margin plus variable costs) per order or customer? Without it, break-even cannot be computed and the verdict may have to be withheld.
7. Are 4-8 prior periods of the same metric, on the same definition, available?

Then three scoping questions, because Step 1's metrics differ by orders of magnitude in effort and in how long their payoff lasts - that ordering cannot be picked for the user:

1. By when must the verdict land - a date, not "soon"?
2. A one-off read, or a standing check that will be repeated every period?
3. What is the effort ceiling: hours available, and whether finance or data can be pulled in at all?

Re-rank Step 1's menus against the answers, and say out loud which answer moved which metric:

• A hard near-term date keeps the run on the near-zero-effort variants (blended CAC, blended ROAS, MER) and deletes fully-loaded CAC, marginal CAC and any margin rebuild from this run - a narrower verdict, on time. Say which variants you deleted and why. A variant left ranked last reappears halfway through as a week of work nobody scheduled.
• A standing check promotes the slow ones: contribution margin, a consistent-definition history, and cohort grouping each cost a week once and near-zero every period after.
• Finance data that cannot produce a variant deletes it outright rather than demoting it: no salary-allocation rule means no fully-loaded CAC, and no contribution margin means no rung 1 either. Name both deletions at intake, and say then that the verdict will be withheld - never at the end of the run.

If you can read the user's exports (CSV, spreadsheet, warehouse extract), work from those. Otherwise ask for the totals per period. Record every answer in the report's definitions section - CAC is not a GAAP or IFRS term, no standards body defines what enters the numerator, so the definition agreed here is the only definition that exists.

Step 1 - Establish the metric variant

"CAC" and "ROAS" each name a family of metrics, not one metric. Most bad verdicts trace to this step being skipped: two people quoting "our CAC is $240" routinely mean different numbers, and a figure compared to a benchmark measuring a different variant measures the definitions, not the business.

Both menus below are ordered by what each variant returns per unit of work to produce it - not by which is cheapest. Compute in that order and stop once the verdict is settled.

• efficiency: blended > new-customer > paid > fully-loaded > marginal
• value (for a health verdict): blended == new-customer > fully-loaded > paid > marginal
• effort: marginal > fully-loaded > paid > new-customer == blended
• compliance cost: fully-loaded > every other variant == none - once it reaches a board deck or an investor update it is a reported figure finance has to own, and redefining it later is a restatement, not an edit.

Marginal CAC's own decision rule (Demand Curve): a rising CAC is not automatically a problem to fix - check contribution margin first, and only test a new channel once the current channel's marginal CAC exceeds what the next channel could realistically deliver. Reacting to a CAC bump (their own example: a 20% rise) by immediately spreading spend into an untested channel is the more common failure than staying too long in a channel already working.

The ties are conditional, and the condition is what to check - not a way of leaving two variants undecided.

• Value tie (blended == new-customer): holds only where the business has no renewals, repeat purchases, or reactivations to miscount. The moment it has any, new-customer CAC sits strictly above blended, because it is the same read with a denominator error removed.
• Effort tie (new-customer == blended): holds only where billing already flags customer status, which makes both of them totals you already hold. Where it does not, new-customer costs a week and drops below paid on the effort line.
• Compliance-cost tie (every variant == none, except fully-loaded): every variant but fully-loaded ties at literally zero, because none of them ever leaves the marketing team's own report.