Ad rotation in Google Ads: Optimize vs Do not optimize

This guide is built from Google Ads Help: Use ad rotation, Organize your account with ad groups, About campaign settings, About responsive search ads, About your Google Ads account limits, Ad Rank, Set up an ad variation and Set up a custom experiment, plus the Google Ads API reference for AdGroupAdRotationMode. How to write the ads themselves is in our responsive search ads guide, and how to run a proper test is in our experiments guide; this page covers the rotation setting only.

What ad rotation decides

Google describes the setting as a way "to specify how often you'd like the ads in your ad group to be served relative to one another." It matters only when an ad group has more than one ad: Google says ads rotate "because no more than one ad from your account can show at a time." So for each auction, Google first picks which of your ads in the ad group enters, and the rotation setting shapes that choice.

The setting exists in Shopping, Search and Display campaigns, and there are two options: Optimize and Do not optimize. The Google Ads API names the same two values OPTIMIZE ("Optimize ad group ads based on clicks or conversions") and ROTATE_FOREVER ("Rotate evenly forever"). Older options you may read about in old blog posts are not in either list.

Optimize

With Optimize, Google "optimizes your ads for clicks in each individual auction using signals (such as keywords, search terms, devices, locations, and more), and prioritizes ads that are expected to perform better than other ads within an ad group."

What that means in practice, according to the same Help page:

• The weighting grows with data. "As data is accumulated, ad serving will become weighted more heavily in favor of the ads that appear statistically likely to perform better."
• The goal is clicks, or clicks and conversions with Smart Bidding. Ads expected to attract more clicks (and conversions if you use a Smart Bidding strategy) enter more auctions and get a higher ad-served percentage.
• Serving can still stay roughly even. Google gives two cases: ads in the ad group perform similarly, or the ad group doesn't get much traffic for a period.
• The choice is per auction. Because it uses the search term, device and location of each auction, an ad that wins on mobile can lose on desktop. The ad-served percentage in the report is an average over all of those auctions.

Google's ad group advice ties the two together: it recommends "at least 3 ads in each ad group and using optimized ad rotation," because "You never know what message might resonate best with potential customers."

Do not optimize

With Do not optimize, "your ads will enter into the ad auction more evenly for an indefinite amount of time." Google states plainly that this option "isn't recommended for most advertisers."

Even rotation is about entering auctions, not about getting the same results. Google warns that the share of impressions per ad "may not be even due to the quality of the ad." Each ad still goes through Ad Rank, which Google says is calculated from your bid, the quality of your ads and landing page, the context of the search and more. In Google's own example, a high-quality ad may show on the first page of results while a low-quality one shows on the second page, where it reaches fewer people. So two ads that enter the same number of auctions can end up with very different impressions.

Smart Bidding forces Optimize

Google's tip on the rotation page: "If you're using Smart Bidding, which prioritizes conversions, Google Ads will automatically use the 'Optimize' ad rotation setting." Smart Bidding covers the conversion-based strategies such as Maximize conversions, Target CPA, Maximize conversion value and Target ROAS (see our budgets and bidding guide). Under those strategies, Optimize also weighs expected conversions, not only clicks.

In other words, Do not optimize only has an effect in campaigns that bid with Manual CPC, Maximize clicks or another strategy that is not Smart Bidding. If you switch a campaign to Smart Bidding, expect ad serving to start favouring some ads, whatever the setting said before.

Campaign or ad group, and where to change it

You can set rotation for a whole campaign or for single ad groups. The Help page's steps (Google Ads interface, current wording):

1. Click the Campaigns icon, open the Campaigns drop-down in the section menu and click Ad groups.
2. Hover over the ad group or campaign and click the settings icon.
3. Click Additional settings, then Ad rotation.
4. Choose Optimize or Do not optimize and click Save.

For several at once, tick the campaigns or ad groups, click Edit and choose Change ad rotation. To find ad groups that use a given setting, use the filter icon, which can filter by ad rotation. In the Google Ads API the field is ad_rotation_mode on the ad group, described as "The ad rotation mode of the ad group."

Ad rotation is listed among the settings in Google's campaign settings overview, and our account structure guide lists it with the other campaign settings.

Rotation vs combinations inside a responsive search ad

In a Search ad group with responsive search ads, two kinds of choosing happen at once:

• Between ads. The rotation setting decides which ad in the ad group enters an auction. An ad group can hold up to 3 enabled responsive search ads, per Google's account limits.
• Inside one ad. Within a responsive search ad, Google "assembles the text into multiple ad combinations" from your headlines and descriptions, and "over time, Google Ads will test the most promising ad combinations." The rotation setting does not switch this off. Pinning is the control for that, and it is covered in our responsive search ads guide.

Google's responsive search ads page reports, as its own averages, that advertisers who went from one responsive search ad to two in an ad group found a 6.6% increase in conversions at a similar cost per conversion, and going from two to three gave an average 3.7% increase. Those are Google's figures across advertisers, not a promise for one account, but they are the reason to give the rotation more than one ad to choose from.

Why even rotation is not an A/B test

A common habit is to set Do not optimize, run two ads and compare them. The Help page explains why that is weaker than it looks: entering auctions evenly does not mean equal impressions, because each ad's quality decides where and whether it shows. The same person can also see both ads on different searches.

Google has two tools built for testing instead:

• Ad variations change headline, description, path or URL text across ads and split traffic "by assigning cookies to users. That means users may discover only one version of your ad, regardless of how many times they search."
• Custom experiments copy a campaign, share its traffic and budget, and let you compare the two versions. Google lists them for Search, Display, Video and Hotel campaigns.

How to set up either, choose the split and read the confidence intervals is in our Google Ads experiments guide.

Which setting to use

Google's recommendation is Optimize for most advertisers, and with Smart Bidding there is no choice. Our own practice, which is our view rather than Google's guidance:

• Leave Optimize on, with 2 or 3 ads per ad group that say clearly different things, so the system has real alternatives.
• Judge ads on click-through rate and conversion rate over the same dates, not on how many impressions each got; under Optimize, impression share is the result of the choice, not a verdict on its own.
• When a question really needs an answer (a new offer, a different call to action), run an ad variation or experiment rather than switching the ad group to Do not optimize.
• If a campaign on Manual CPC or Maximize clicks uses Do not optimize, write down why. Settings like this tend to stay long after the test that needed them is over.
• Replace weak ads instead of leaving them in place; Optimize will mostly stop serving them anyway, so they add little.

Frequently asked questions

What is the difference between Optimize and Do not optimize in Google Ads?

Optimize favours the ads in an ad group that are expected to get more clicks (and conversions with Smart Bidding) in each auction. Do not optimize lets the ads enter auctions more evenly for an indefinite time, though impressions can still differ because of ad quality.

Can I use Do not optimize with Target CPA or Maximize conversions?

No. Google says that with Smart Bidding, Google Ads automatically uses the Optimize setting. Do not optimize only applies under strategies that are not Smart Bidding, such as Manual CPC or Maximize clicks.

Is ad rotation set at campaign or ad group level?

Both. You can set it for a campaign or for individual ad groups from Additional settings, and change many at once with Edit, then Change ad rotation. In the API it is the ad_rotation_mode field of the ad group.

Why does one ad get most of the impressions under Optimize?

Because Google weights serving towards the ads it expects to perform better, and that weighting grows as data comes in. If ads perform similarly or traffic is low, serving can stay fairly even.

Should I use Do not optimize to test ads?

Google does not recommend it for most advertisers, and impressions are not even under it anyway. Ad variations, which split users by cookie so each person tends to see one version, are the tool Google provides for testing ad text.

For more on Google Ads, see our guides to responsive search ads, experiments, budgets and bidding, Quality Score and account structure.