Managing Google Ads by Contribution Margin
A high ROAS does not tell you whether a shop makes money with Google Ads. I restructure the Google Ads accounts of online shops so that bids and budgets follow the contribution margin: what is left after goods, shipping, fees, returns and advertising.
Why revenue is the wrong target.
Smart Bidding optimises for the conversion value that the account reports. For almost all shops, that is revenue. Google therefore treats one euro of revenue from a product with a 15 per cent margin the same as one euro from a product with a 60 per cent margin. The account grows, but profit does not necessarily.
The floor for every target is the break-even ROAS: value per order divided by the contribution margin per order before advertising and after returns. An example with a net value of €100 and a contribution margin of €27.25 gives 3.67, or 367 per cent. Below that, every order loses money. The calculation with all costs is in the article Calculating break-even ROAS, with the costs that are often missing.
The changeover in four stages.
I only go as far as it pays off for your shop. The next stage only makes sense if the differences in margin actually change the ranking of your products.
Assess products
Contribution margin per product from purchase price, shipping, payment fees and return rate. From that, the break-even ROAS per product or group.
Margin groups with their own target
Products get custom labels by margin class and run in campaigns with their own target ROAS. This is possible with any shop system and is enough for many shops.
Margin as conversion value
Instead of revenue, the shop reports the gross margin per order to Google, using server-side tracking if needed. Smart Bidding then optimises directly for gross profit.
Contribution margin after returns
For shops with high returns: a deduction per category or a retroactive correction of the conversion values. Only this stage reflects the result after all variable costs.
What this looks like in a real account.
For XXL-Parfum.ch I built a margin system that assesses over 17,000 products daily by contribution margin and aligns bids accordingly, together with automatic repricing. After the restructuring, ROAS rose from 381 to 442 per cent. More important than the figure is the gap to the break-even of 310 per cent: it shows how much is left after ad spend. Period: January to mid-April compared with the period from 24 April 2026, Google Ads data.
A single client case, no promise for your account. More under Results.
Further reading
Frequently asked questions.
What is the difference between ROAS and POAS?
ROAS is revenue divided by ad spend. POAS is contribution margin before advertising divided by ad spend, which works out as ROAS times order margin. POAS only leads to better bids if the margin varies clearly between orders. With the same margin, a converted ROAS target produces the same bids.
Do I have to send purchase prices to Google?
Not for margin groups: the labels only tell Google which class a product belongs to. Only when the margin is reported as conversion value does it flow into the data of your Google Ads account. We decide that together.
What data do you need for this?
Purchase prices or margins per product, shipping and payment costs, return rates per category. A spreadsheet from your inventory management system is enough to start with. If something is missing, we estimate with transparent assumptions and replace them later.
For which shops does this not pay off?
If almost all products have a similar margin, the changeover changes little. In that case, a target ROAS above break-even is enough. I will tell you that after the audit.
The entry point: a free audit.
You invite me as a read-only user into your account, two clicks, revocable at any time. I take apart structure, bidding, PMax, feed and tracking, build you a dashboard with your key figures, and give you a written roadmap plus a 30 to 45 minute call. Everything is yours, whether we work together afterwards or not.
Or write directly to stefan@stefanriemeyer.com or send a message on LinkedIn. You write to me, not to an inbox team. The roadmap arrives within a few working days.
Prefer to talk first? Book a 30-minute intro call.