Definition
Audience overlap is the share of users who fall into two or more of an advertiser's targeting segments, campaigns or ad sets at the same time. When overlap is high, those campaigns are effectively bidding against each other for the same people in the platform auction.
The advertiser pays a higher price than necessary because it is its own competition, delivery becomes uneven as the platform arbitrarily picks which of your ad sets serves a given user, and per-campaign performance data is distorted because a conversion that any of the overlapping campaigns could plausibly claim gets attributed to just one of them.
Overlap appears whenever segments are defined loosely or built from related seeds: a broad interest set and a narrower one on the same theme, a lookalike audience and an interest audience that describe similar people, or a retargeting pool that has not been excluded from prospecting campaigns. On large platforms it is common to discover that two "separate" audiences share 40% or more of their users once you actually measure it.
In context
Ad platforms provide overlap reports that show, for any pair of audiences, the percentage of shared users. The fix is structural: merge two heavily overlapping ad sets into one so the platform optimises across the combined pool instead of splitting budget and signal, or add explicit exclusions so each audience is mutually exclusive — prospecting excludes site visitors, one interest set excludes the other, retargeting excludes recent converters.
Both approaches reduce internal competition, which typically lowers CPM and stabilises delivery.
In iGaming this matters most when running lookalikes of depositors, broad interest targeting and retargeting for the same brand simultaneously, which is a normal setup. Cleaning overlap also makes attribution honest: with mutually exclusive audiences, a conversion belongs unambiguously to one campaign, so the buyer can trust the cost-per-FTD comparison between them and cut the genuine losers rather than the ones that merely lost an internal attribution coin-flip.
Worked example
An overlap report shows two interest-based ad sets for the same casino share 46% of their users. The buyer merges them into a single ad set with the combined budget.
Over the next week CPM drops 18%, daily FTDs are unchanged, and the cost-per-FTD figures for the remaining ad sets become stable enough to act on.
Frequently asked questions
Browse the full iGaming & affiliate glossary — hundreds of EN/RU terms with examples.
← Back to glossary