What is incremental ROAS?
Incremental ROAS, or iROAS, is the return on only the sales your ads actually caused. It strips out the revenue that would have arrived anyway and credits the campaign with the genuine lift.
It exists because reported ROAS is usually too generous. Attribution hands ads credit for customers who were already going to buy, so a campaign can show a strong ROAS while adding very little.
The formula.
Incremental ROAS = incremental revenue ÷ incremental spend. The hard part is the numerator: the lift has to be measured, not assumed.
This tool offers two ways. Enter the lift directly if you already have it, or enter revenue with ads against a baseline without them and let the tool find the difference.
A worked example.
Ads cost 10,000 and lift revenue from a 100,000 baseline to 130,000. The incremental revenue is 30,000, so incremental ROAS is 30,000 ÷ 10,000, which is 3x.
What is a good incremental ROAS?
Anything above 1x means the ads returned more than they cost in true-incremental terms, and 3x and up is strong. The number is almost always lower than reported ROAS, which is the point: if reported ROAS looks fine but incremental ROAS sits below 1x, the spend is buying sales you already had.
Reported ROAS and incremental ROAS tell different stories about the same spend. Seeing them side by side is the fastest way to find whether the unit economics hold.
How to improve it.
Shift budget toward audiences and campaigns that show real lift in a holdout, and cut the ones that only harvest existing demand. Prospecting usually carries more incremental value than branded retargeting.
The demand that ads merely harvest has to come from somewhere first. Organic search and content create it, giving you a channel mix that compounds.