Why Platform ROAS and CFO MER Disagree

Google Ads reports ROAS. Your CFO cares about MER. These are not the same metric and the two views diverge by a wide margin in most multi-location eye care accounts. ROAS as Google reports it is platform ROAS, the revenue Google’s attribution model credits to its own ad clicks divided by the spend on those ad clicks. MER, the Marketing Efficiency Ratio, is total practice revenue divided by total marketing spend across every channel the practice runs. The first view captures within-platform efficiency; the second captures whole-business efficiency.

The reason the two views diverge so much is that platform ROAS is structurally generous. Google credits itself with the conversion any time a user clicked a Google ad in the attribution window, even when the user would have converted anyway through organic search, direct navigation, or a referral. MER does not care about attribution because it does not assign credit, it simply asks how much revenue the practice generated against how much it spent on all marketing combined. The structural difference is what makes MER the right primary metric at the CFO level and ROAS the right secondary metric at the platform-optimization level.

How Each Metric Is Defined and What Each Captures

Platform ROAS, as Google Ads reports it, is the revenue attributed by Google’s attribution model divided by Google Ads spend. The attribution model since 2024 is data-driven attribution by default, which distributes conversion credit across touchpoints using a probabilistic model. For accounts with offline conversion imports, the revenue numerator includes those imports; for accounts without, only online-attributed revenue counts. The denominator is straightforward, the platform knows what it spent.

MER is total revenue divided by total marketing spend across all channels. The numerator comes from the practice’s financials, not from any marketing platform, and includes revenue regardless of how it was generated. The denominator includes paid ad spend across Google, Meta, and any other platform, plus agency fees, plus marketing tool subscriptions, plus an allocated cost for SEO content production, plus offline marketing if the practice runs any. The ratio is intentionally attribution-agnostic, MER is not trying to assign credit, it is measuring whole-business marketing efficiency.

The captured information differs accordingly. Platform ROAS captures whether you are spending efficiently within a channel and supports within-channel optimization decisions. MER captures whether the marketing function as a whole produces efficient returns and supports portfolio-level allocation decisions. Using one when the other is required is the structural cause of most marketing-allocation mistakes in multi-location healthcare groups.

What Healthy MER Ranges Look Like for Eye Care

Ecommerce MER benchmarks land in a 3:1 to 5:1 range as healthy, with anything below 2:1 triggering portfolio review. Healthcare MER benchmarks are less standardized in published sources, the data gap exists because most healthcare organizations either do not track MER consistently or treat it as a private financial metric rather than a published benchmark. For multi-location eye care groups specifically, mature accounts typically run 4:1 to 8:1 MER, with the upper end concentrated in groups that have strong organic search and referral channels supplementing paid acquisition.

The MER-to-ROAS ratio is itself a diagnostic. Google Ads ROAS commonly runs 1.5 to 3 times the MER number because Google’s attribution model counts last-touch and assisted conversions as fully its own. The gap widens further when offline channels are large, a practice that runs an active referral marketing program, brand events at school districts and pediatricians, or substantial organic SEO investment is generating revenue that supports the paid conversion but sits entirely outside Google’s attribution window, so platform ROAS keeps the credit while MER alone reflects that the rest of the marketing portfolio did the work. As that ratio grows, the platform reporting is overstating the platform’s contribution and the CFO-level view is becoming more important. Watch the ratio quarter over quarter, a stable ratio is fine; a growing ratio means the agency is reporting efficiency that the practice’s financials do not see. For supporting performance baselines, see our PPC benchmarks for eye care.

The Red Flags That Signal MER Is Not Being Tracked

Five red flags indicate the marketing function is being run on platform ROAS without a CFO-level MER view. The first is an agency that reports ROAS only and never references MER, which means channel-allocation decisions are being made with incomplete information. The second is a stated reason for not calculating MER, usually “the attribution is too complex,” which misunderstands the metric, MER is precisely the metric that does not require attribution. The third is ROAS reported without explanation of which attribution model produced the figure, the same ad spend can produce ROAS figures that vary by 50 percent or more depending on whether the model is last-click, data-driven, or platform-default.

The fourth is a CFO who never receives a marketing-to-revenue view in any standardized format, the marketing team reports campaign metrics and the CFO reports financial metrics and the two never reconcile. The fifth is the absence of a year-over-year MER trend, which is the single most useful longitudinal marketing metric a multi-location group can maintain. Worth singling out is the “too complex to attribute” deflection, which is structurally false, MER does not require attribution at all, the calculation is total revenue divided by total spend and the inputs come from the financial system rather than from any marketing platform. The agency that frames MER as too complex is signaling that they do not want to be held to a portfolio metric that flattens their platform-ROAS narrative; it is a positioning move rather than a methodology limitation. Without a year-over-year MER trend the practice cannot tell whether marketing efficiency is improving or eroding over time, and channel-mix decisions become reactive rather than strategic.

How to Stand Up MER Reporting Quarterly

Calculate portfolio MER quarterly. Pull total practice revenue from the financial system over the trailing 90 days. Pull total marketing spend over the same window from every source: ad spend by platform, agency retainers, tool subscriptions, allocated SEO and content costs, and offline marketing if applicable. Divide the first by the second. Report the figure alongside platform ROAS in any CFO-facing marketing report, and chart the trend across at least four quarters so the trajectory is visible.

Watch the MER-to-ROAS ratio explicitly. If platform ROAS rises while MER stays flat or declines, the platform is taking credit for revenue that would have happened anyway, the optimization narrative is disconnecting from business reality. The discipline of standing the metric up quarterly typically takes one analyst-day per quarter and produces the most consequential reframing of marketing reporting most multi-location groups will encounter. Build the quarterly review around three artifacts: a single-page MER trend chart over the trailing four quarters, a side-by-side comparison of each channel’s reported ROAS against the portfolio MER, and a brief written commentary explaining any divergence between the two views. The chart prevents the conversation from drifting back into platform-only metrics during the meeting itself, and the written commentary gives the next quarter’s review a baseline to compare against. For supporting context, see data-driven attribution, offline conversion imports, value-based bidding, and good Google Ads management.

Specialty Vision’s Take

Our view is that the practices governing marketing at MER level make better channel-allocation decisions than those governing at platform-ROAS level. MER forces honest trade-offs between paid and organic and between Google, Meta, and email. Platform-ROAS encourages spending more on the highest-ROAS platform without acknowledging diminishing returns or channel cannibalization. PE-backed multi-location groups especially benefit from MER governance because portfolio-level allocation across channels is structurally where the marketing-efficiency wins live, and platform-only reporting cannot see the portfolio. The lead-quality blind spot is closely related, see our piece on the lead-quality blind spot; CPL-only reporting is the symptom and platform-ROAS-only reporting is the underlying frame. Quarterly is the right cadence, frequent enough to catch drift, infrequent enough that it does not become noise. For the broader benchmark context, see the specialty eye care PPC benchmarks report.