Free tool
Audience overlap calculator
When two of your audiences overlap, the ad sets bid each other's CPM up. Estimate how much that self-competition is costing you each month.
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Free tool
When two of your audiences overlap, the ad sets bid each other's CPM up. Estimate how much that self-competition is costing you each month.
Want this running 24/7 on your account?
Audience overlap is the share of people who sit inside two of your targeting definitions at once. It matters because Meta runs one auction per impression opportunity. If two of your ad sets both want the same person, they can both bid — and the price one of them pays is set partly by the other. You end up buying reach you already owned, at a worse rate.
Overlap is not automatically bad. A retargeting ad set and a prospecting ad set that share a few percent of people are doing different jobs. The problem is scale: once a large share of your combined reach is the same people seeing the same offer, the second ad set is mostly buying frequency, not incremental reach.
You enter both audience sizes, your estimate of the overlap as a percentage of the smaller audience, and the combined monthly spend of the two ad sets. From that the tool computes the overlapping headcount (smaller audience × overlap%), the total unique reach (A + B − overlap), and the overlap share — the double-targeted people as a fraction of that unique total.
The cost band is deliberately conservative: it assumes 25% to 50% of the overlap-weighted spend is lost to bidding against yourself, and reports the range rather than a single number. The remaining spend still reaches unique people and still does its job. Treat the low end as the floor and the high end as the realistic case when both ad sets carry the same offer.
Because Meta no longer publishes a measured overlap figure, the accuracy of the output is bounded by the accuracy of the percentage you type in. It is a sizing exercise — is this a $60/month problem or a $2,000/month one — not a measurement.
High risk (30%+ of combined reach) has two fixes. Consolidate: merge the two ad sets so one budget and one learning phase cover the shared audience. Or exclude: add each audience as an exclusion on the other so a person can only be reached by one. Consolidation is usually better when the two ad sets run the same offer, because it also concentrates conversion volume and helps the ad set exit the learning phase faster.
Moderate risk (15–30%) is worth an exclusion if the offers match and worth ignoring if they do not. Low risk needs no action. Either way, if the two ad sets are also both expensive relative to the account, run the cannibalization detector — overlap plus above-median CPL on both sides is the signature of a genuine cannibal pair, and the wasted-spend guide covers the rest of the leaks.
Last updated August 31, 2026. All 17 calculators and AI helpers are listed on the free tools hub.
FAQ
This calculator draws the line at 30% of combined reach for high risk and 15% for moderate. Below 15% the two audiences are distinct enough to run side by side. Above 30% you are systematically bidding against yourself in the same auctions, and consolidating the ad sets or adding mutual exclusions almost always beats leaving both running.
No. Meta retired the standalone Audience Overlap report, which is why this tool asks you to estimate the overlap yourself rather than pretending to measure it. Estimate from what you know about the definitions — two lookalikes off the same seed overlap heavily, a 7-day retargeting pool and a cold interest stack barely overlap at all.
When two of your ad sets target the same person, both can enter the same auction for that person's impression, and the winning bid is set against the other. You pay more for reach you would have won anyway. The size of that effect depends on how much of your delivery lands on shared people, which is exactly what the overlap-share figure estimates.