Incremental ROAS (iROAS)

What iROAS actually means

Standard ROAS counts every conversion the platform can claim, including customers who were going to buy anyway. Incremental ROAS counts only the lift. The distinction matters most in the channels that look best on paper: branded search, retargeting and shopping ads all harvest demand that already exists, so their reported returns usually overstate their true contribution by a wide margin.

Worked example

A retargeting campaign reports 8.0 ROAS on 50,000 dollars of spend, implying 400,000 dollars of attributed revenue. A geo holdout shows test regions generated 320,000 dollars while matched control regions generated 250,000 with no retargeting at all. The incremental revenue is 70,000 dollars, so iROAS is 1.4, not 8.0.

Why the board cares

Incrementality is how a board finds out whether the marketing budget is buying growth or buying credit for growth. The first time a company runs a proper holdout on branded search, the result is usually uncomfortable and always useful. Boards increasingly expect at least one incrementality test per major channel per year.

Common mistakes

• Running a holdout too short to cover the full purchase cycle, which reads delayed conversions as lost ones.
• Using unmatched control groups, so the difference measures geography rather than advertising.
• Testing only the channels expected to pass, which turns measurement into confirmation.

Related terms

• Return on Ad Spend (ROAS)
• Incrementality Testing
• Marketing Efficiency Ratio (MER)
• Multi-Touch Attribution (MTA)

Back to the full marketing glossary