---
title: Holdback: Measure overall impact in Personalization
slug: personalization/docs/holdback-measure-overall-impact-in-personalization
docTags: 
createdAt: 2026-08-05T20:59:36.639Z
---

Every Optimizely Personalization [campaign](docId\:IRPnddq1sAJsB7qDhi4LB) has a holdback, the control of an A/B test. Optimizely's [Stats Engine](../../experimentation-strategy/measure-and-analyze-results/statistical-concepts/calculate-the-statistical-likelihoods-of-variations-using-stats-engine.mdx) uses the holdback to help you track how well your personalized experiences perform compared to the generic experience.

By default, Optimizely Personalization shows a personalized experience to 95% of campaign visitors and holds back 5% who see the original.

Visitors are bucketed into the holdback by chance.

Holdbacks are persistent. When a visitor is bucketed into the holdback, they always see the holdback experience for that campaign.

![targeting-25.png](https://api.archbee.com/api/optimize/BrbvVORKJ5iIeSMZye5kI/fKram-H7HhfcNFcF9-NXP-20260720-150058.png)

Managing the balance between too big of a holdback and too small can be confusing. Five percent holdback is the industry standard because it is a good balance and lets you monitor how well your campaign is doing.

A larger holdback may not help you gather data about [statistical significance](../../experimentation-strategy/measure-and-analyze-results/statistical-concepts/statistical-significance.mdx) faster. Instead, you risk underpowering your experiment. An experiment that is too underpowered may be inconclusive. Your traffic is finite, and having a large holdback prevents a large amount of traffic from seeing the personalized experience.

## Set the holdback

When you [create a campaign](docId\:NkIwGDwaT_OBnqlWD92ns), set the holdback in the final step.

:::hint{type="info"}
**Note**

Stats Engine does not support changing the holdback for a running campaign. If you choose to do this, you may see invalid statistical reports.
:::

Optimizely Personalization sets one holdback per campaign. The holdback stays the same no matter how many experiences or variations you add to a campaign.

1. Go to **Optimizations** and select the campaign.
2. Click **Settings**.

   ![EditHoldback.png](https://api.archbee.com/api/optimize/BrbvVORKJ5iIeSMZye5kI/rhl0oz1en1RJ4Beiykw03-20260720-150058.png)
3. Edit the holdback.
4. Click **Save**.

To reset the holdback, click **Revert**.