When Google and Meta both claim the same sale

Add up the conversions Google and Meta each report, and you will often find you sold more than you actually sold. The extra sales are not real. They are the same customer, counted twice.

Here is how it happens. A customer sees a Meta ad early, then later clicks a Google ad and buys. Google saw the last click and claims the sale. Meta saw the earlier touch and claims it too. Each platform is telling its own truth, and neither tells you the other did the same. So your combined performance is quietly inflated by a number nobody prints, and you end up budgeting against revenue that partly does not exist.

For years the only response was to pick an attribution model and argue about it. That is a real debate, and a genuinely hard problem, but it does not help you on a Tuesday when you just need to know what the account actually earned across everything.

Blended ROAS steps back to a simpler, sturdier question: total revenue, total spend, across every platform, counted once. It does not try to adjudicate which platform "deserves" the sale. It just refuses to count the sale twice. And a double-count signal flags where the platforms are overlapping, so you can see how much of your reported success is the same customer wearing two hats.

On sample data, the inflation is easy to see. Add up what each platform claims, then compare it to what actually happened at the checkout:

Sample data, for illustration.

Seventy orders exist twice — once in Google's column, once in Meta's. At €30,000 of total spend, the sum-of-claims view reports a 2.67× ROAS on revenue that partly does not exist, while blended lands at 2.2× on revenue that does. The double-count signal is just that overlap row surfaced on purpose: 17.5% of the "wins" were the same customer, seen twice. Budget against the 2.67× and you are funding phantom revenue.

It is less flattering than the sum of the in-app numbers. A blended view almost always looks worse than adding up what each platform claims, because the in-app numbers were overlapping all along. Less flattering, and true.

Multi-touch attribution is coming to go deeper on this. Until then, blended is the honest, available answer. The pillar is Find the money you're burning, and tomorrow reaches the number underneath it all in What actually lands in the bank.