Free tool
Incremental ROAS Calculator (iROAS)
Your ROAS counts the sales your ads saw. Incremental ROAS only counts the ones they caused. Enter your test results: the tool shows you the gap.
Incremental ROAS (iROAS) is the extra revenue generated by each unit of ad spend. Google calculates it by subtracting the conversion value of the control group, which did not see the ads, from that of the treatment group, then dividing by spend. Standard ROAS divides all attributed conversion value by spend.
What your ads really created
How incremental ROAS is calculated
Incremental revenue = Treatment revenue − Control revenue × (treatment size ÷ control size) Incremental ROAS = Incremental revenue ÷ Spend
Using the figures from Google’s example, in euros: 20,000 € of revenue in the treatment group, 10,000 € in the control group, 5,000 € of spend. Incremental revenue is 10,000 € and incremental ROAS is 2.
Picture a poster outside a bakery at 7 am. Customers walk in, and the poster can claim every one of them. Most would have come anyway. The control group is there to count those people: the sales your campaign would have had without spending anything.
If your control group is smaller than the treatment group, its revenue is scaled up before the subtraction: the tool does it from the size you enter. At 50 %, both groups are the same size and the formula becomes Google’s again.
What incremental ROAS changes in your decisions
- It is not marginal ROAS. In my article on marginal ROAS, I look at what the last euro spent brings in. Incremental ROAS asks another question: what the ads caused, in total, compared with spending nothing.
- It separates two campaigns with a similar reported ROAS. A campaign that reaches customers who had already decided can show a very good ROAS while causing few sales, and that is exactly what a test lets you check.
- It is measured, not guessed. Google Ads offers Conversion Lift studies that create the control group, and Meta offers holdout tests. Without a control group, no calculation can tell what would have sold without the ads.
Your ROAS looks good, but what do your ads really bring in?
That is the question to ask before raising a budget. Let’s talk about what your campaigns actually cause.
Measure My Real ROAS
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Théo MaupiléFreelance Paid Media
Google PartnerSuperMalter
