> For the complete documentation index, see [llms.txt](https://docs.mediarithmics.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.mediarithmics.io/audience-and-activation/analyze-your-data/overlap-segments.md).
# Overlap segments
Find out which segments share the most users with the one you are working on, and what to do about it.
## Your goal
Find out how much an audience is already covered by your other audiences, and use that to decide whether to expand it, exclude it, or leave it alone.
## Expected outcome
An overlap analysis on the segment, showing the 20 segments sharing the most users with it, and a decision taken from it.
## When this is useful
* **Before expanding a segment.** If most of the seed already sits inside a much larger segment, a [lookalike](/audience-and-activation/build-your-audiences/expand-your-audience-with-lookalike.md) may add little that you do not already address.
* **Before buying media.** Two segments that overlap heavily will produce duplicated exposure if you target both.
* **When building exclusions.** Overlap tells you which audience is worth excluding from a campaign.
* **When a segment behaves oddly.** Heavy overlap with a segment you did not expect often reveals a query that is broader than intended.
## Steps
{% stepper %}
{% step %}
### Create the analysis
On the segment page, click **Create Overlap Analysis**.
{% endstep %}
{% step %}
### Filter by label (optional)
Once the analysis has been computed, use **Filter by label** to display only the segments carrying the [labels](/audience-and-activation/build-your-audiences/segment-reference/segment-capabilities/labels.md) you select. You can select several labels. The filter changes what the chart displays, not the analysis itself, which runs on all the segments of your datamart.
{% endstep %}
{% step %}
### Read the chart
You get a bar chart of the 20 segments sharing the most users with the current segment, sorted by percentage of shared users. Hold the pointer over a bar to see the segment's full name and the percentage of common users.
{% endstep %}
{% step %}
### Refresh when needed
The chart shows the data as of the moment the analysis ran; the timestamp is in the top right corner. Press **Refresh** to recompute.
{% endstep %}
{% endstepper %}
## Reading it correctly
The percentages are calculated against the **total number of users in the current segment**, not against the other segment's size. That makes overlap directional.
{% hint style="warning" %}
**Worked through.** A segment of 10,000 users entirely contained in a segment of 1,000,000 shows as **100%** when you run the analysis from the small segment, and as **1%** when you run it from the large one. Both are correct, and they say different things. Run the analysis from the segment whose audience you are trying to explain.
{% endhint %}
The mechanics of the computation are documented in [Overlap](/audience-and-activation/build-your-audiences/segment-reference/segment-capabilities/overlap.md).
## Verification
The analysis completes and the timestamp updates. If a segment you expected is absent from the chart, it either shares fewer users than the twentieth-placed segment, or it is not persisted - a segment whose membership is not stored cannot be compared.
## Related pages
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