ROAS measures how many dollars of revenue a campaign returned for every dollar spent on advertising. It does not measure how many dollars of margin that revenue produced. On a product with a gross margin below fifty percent, a 4x ROAS can generate less than a dollar of gross profit per ad dollar spent once fulfillment, merchant fees, and return costs are deducted. At that ratio, scaling ad spend scales revenue and destroys margin simultaneously.

Campaigns are directed toward the audiences and placements that generate the highest revenue return. Those are not necessarily the audiences generating the highest margin return. A brand selling products at different price points will find its ad spend concentrating on high-revenue, low-margin SKUs because those are the ones that make the ROAS number look strong. City Shift Finance has analyzed how the contribution margin below the gross margin line tells a different story than the revenue number the campaign is optimizing for. This is also a core driver of the ecommerce SKU profitability misreading that leads brands to over-invest in products that are destroying cash.

The financial strain compounds when the payback period on customer acquisition is calculated against revenue rather than contribution margin. Capital that the business expects to return in approximately sixty days may take two to three times longer to materialize once the true contribution margin per acquired customer is used as the baseline.

As the brand scales ad spend, the absolute dollar value of that gap grows proportionally. The advertising costs consuming contribution margin at the unit level will eventually consume the balance sheet if the payback period is never measured against the correct baseline.

The advertising dashboard will always show a number that looks like progress. The contribution margin statement shows what that progress actually cost.