WhyYourGoogleAdsROASIsLyingToYou-AndWhatToMeasureInstead

ROAS is the most widely reported metric in ecommerce Google Ads. It is also, in many accounts, the most misleading. A 4x ROAS sounds like a success story. At a 20% gross margin, it is a loss. This is not a fringe case. It is happening in accounts across the industry right now - while the monthly report says "strong performance."

The problem with ROAS

Return on Ad Spend is calculated as revenue divided by ad spend. If you spend £10,000 and generate £40,000 in revenue, your ROAS is 4x. Simple. Clean. Easy to report.

It is also, in isolation, commercially meaningless.

ROAS measures the efficiency with which your ad spend generates revenue. What it does not measure - what it has never measured - is whether that revenue is profitable. It contains no information about your cost of goods. No information about your fulfilment costs. No information about your return rate. No information about the margin that sits between the revenue number and the cash that actually reaches your business.

This distinction matters enormously. Consider two brands, both running Google Ads at 4x ROAS.

Brand A operates at 40% gross margin. Their break-even ROAS - the point at which ad spend breaks even against the gross profit it generates - is 2.5x. At 4x ROAS, they are comfortably profitable on their ad spend. They have room to scale, room to discount, room to absorb a spike in CPCs without the economics collapsing.

Brand B operates at 20% gross margin. Their break-even ROAS is 5x. At 4x ROAS, they are losing money on every single order generated by Google Ads. The revenue is going up. The cash position is getting worse. And the monthly report is saying "strong performance."

Both brands are hitting 4x ROAS. One is building a business. The other is funding a very expensive illusion.

Where does break-even ROAS come from?

Break-even ROAS is the ROAS at which the gross profit generated by ad spend exactly covers the ad spend itself. Below it, you lose money on every Google Ads conversion. Above it, you generate profit. The formula is straightforward:

Break-even ROAS = 1 ÷ Gross Margin %

• At 40% gross margin: break-even ROAS = 2.5x
• At 30% gross margin: break-even ROAS = 3.3x
• At 25% gross margin: break-even ROAS = 4.0x
• At 20% gross margin: break-even ROAS = 5.0x
• At 15% gross margin: break-even ROAS = 6.7x

This number should be the foundation of every Google Ads target you set. It is the commercial floor beneath which your advertising strategy loses money regardless of how good the ROAS looks in the report.

Most ecommerce brands running Google Ads do not know this number. Their agencies have not calculated it. Their ROAS targets were set in an onboarding call based on what sounded commercially reasonable - or, more commonly, what the client said they needed to hit to justify the spend - and have not been revisited since.

This is not a minor oversight. It is the central failure of most Google Ads management.

The discount problem

The gap between ROAS and profitability becomes most dangerous - and most visible - during sale periods and promotional events.

Consider a brand with a standard 40% gross margin running a 20% discount during a promotional event. The discount compresses their margin from 40% to 25% overnight. Their break-even ROAS moves from 2.5x to 4.0x.

If their agency's ROAS target is set at 3x - which looked healthy under normal trading conditions - they are now running a loss-making campaign during their highest-spend period of the year. CPCs spike during sale periods as every competitor enters the auction simultaneously. So their cost per conversion goes up at precisely the moment their margin per conversion goes down.

The account hits 3x ROAS. The report is sent. The agency calls it a successful peak period.

In January, the brand wonders where the cash went.

Why agencies don't tell you this

The question worth asking is: if this is so foundational, why do so few agencies ever raise it?

Part of the answer is structural. Most agencies charge a percentage of ad spend. Their fee increases when the budget increases. Their fee is unaffected by whether the spend is profitable. The metric that governs their commercial success - client retention - is served by monthly reports that look good and clients who feel the account is being managed. ROAS is a metric that can be made to look good without any connection to the client's actual unit economics.

Part of the answer is competence. Calculating break-even ROAS and managing to it requires understanding the client's P&L, building it into the account structure, revisiting it when margin changes, and applying it at product level rather than as a blended account target. This is harder than moving a ROAS slider. Many agencies have not built the capability to do it properly.

Part of the answer is the pitch dynamic. Agencies win business by presenting confident strategies and ambitious targets. "We need to understand your gross margin before we can tell you what a profitable ROAS target looks like" does not win pitches the way a slide deck with projected revenue figures does. So agencies stop asking. And the question disappears from the conversation.

What remains is a very detailed report about a metric that does not tell you whether your advertising is making you money.

POAS: the metric that actually matters

Profit on Ad Spend (POAS) is the metric that connects your advertising directly to your commercial performance. Where ROAS divides revenue by ad spend, POAS divides gross profit by ad spend.

POAS = Gross Profit ÷ Ad Spend

A POAS above 1.0 means your ad spend is generating more gross profit than it costs. A POAS below 1.0 means every pound spent on advertising is destroying margin.

This is the number your agency should be targeting. Not ROAS. Not blended revenue. Not impression share or CTR or quality score. The ratio of gross profit to ad cost, measured at campaign level, at product category level, and ideally at SKU level for your highest-spend lines.

The transition from ROAS to POAS requires one input that most agencies have never asked for: your gross margin data. Not estimated. Not blended across the entire business. Actual contribution margin by product or product category, updated when your costs change, applied specifically to the campaigns and product groups that are being optimised.

With this data, the account can be structured around profit rather than revenue. High-margin products get aggressive targets. Low-margin products get tight floors or exclusions. Promotional periods get recalibrated targets that reflect the compressed margin of the sale. The account stops generating impressive ROAS and starts generating actual profit.

What SKU-level profitability actually looks like

The most common version of this problem in practice: a brand with a catalogue of several hundred SKUs, managed through a single Shopping campaign or a consolidated Performance Max campaign, with one ROAS target applied across every product regardless of margin.

In this setup, Google's algorithm optimises toward products with the strongest conversion signal - typically the brand's best-selling SKUs, which have accumulated the most historical data. These products receive the majority of the budget. They convert well. The ROAS looks strong.

But best-selling SKUs are not always the highest-margin SKUs. In many catalogues, the products that sell most reliably are mid-range items with moderate margins. The high-margin products - often newer lines, more premium price points, or less established categories - have less historical data, receive less budget, and are progressively starved of signal by an algorithm that rewards conversion volume rather than profit contribution.

The result is an account that generates strong ROAS by systematically advertising the wrong products at scale. The revenue looks good. The margin quietly erodes. And the management fee arrives on the first of the month regardless.

Fixing this requires margin data applied at SKU or product category level, campaign segmentation that separates product tiers by profitability, and bid targets derived from break-even ROAS for each tier rather than a single blended target across the account.

The return rate adjustment

There is a further adjustment that almost no agency makes: return rate.

If your account reports a conversion when an order is placed - as most do - your ROAS includes revenue from orders that will subsequently be returned. For fashion and apparel brands, return rates of 20-35% are common. For some categories and price points, higher.

If 25% of your revenue reverses through returns, your effective ROAS is 25% lower than reported. A campaign showing 4x ROAS is actually performing at 3x on net revenue. If your break-even ROAS is 3.3x, a campaign that looks profitable is actually losing money - and every optimisation decision made on the reported figure has been made on data that does not reflect reality.

The correct calculation builds return rate into the break-even ROAS. If your gross margin is 40% and your return rate is 25%, your effective margin on net revenue is approximately 30%, making your break-even ROAS on net revenue 3.3x rather than 2.5x. Every campaign running below that figure on net revenue is loss-making, regardless of what the reported ROAS says.

Making the transition

Transitioning from ROAS-based management to POAS-based management is not complicated. It requires three things that most brands already have access to.

First: Your gross margin by product or product category. This should come from your P&L or your Shopify cost data. It needs to be accurate, not estimated, and it needs to reflect your actual COGS rather than your retail margin. When supplier costs change, this number needs to change with them.

Second: Your return rate by product category. This is available in your Shopify analytics. It needs to be segmented by category because return rates vary significantly - your footwear line may return at 35% while your accessories return at 8%.

Third: Campaign segmentation that maps to your margin tiers. High-margin products in one group with an aggressive POAS target. Mid-margin products in another with a moderate target. Low-margin products either excluded or given a hard floor below which spend stops.

With these three inputs, the account can be managed to commercial reality rather than to revenue optics. The reports will look different. The ROAS figures will often be lower, because you have removed the low-margin conversions that were pulling it up. But the profit per order will be higher, and the cash position will improve.

That is the point of the exercise. Not impressive numbers in a monthly report. Actual profit from your advertising spend.

The honest conversation

Most agencies will not initiate this conversation. The reasons are structural, commercial, and - in many cases - a reflection of genuine gaps in capability. Asking the margin question, building it into the account, and reporting on profit rather than revenue requires more work, creates more difficult conversations, and generates reports that are harder to celebrate.

It also produces better outcomes for the brands involved.

If you have been running Google Ads without a break-even ROAS calculation, without margin data in your account structure, and without product-level profitability reporting - start there. Calculate the number. Share it with your agency. Ask them to recalibrate every target in the account from it.

Their response will tell you a great deal about the quality of what you have been receiving.