KPI Monitoring & Diagnosis: Why Does Your CTR Change Over Time?

By Brad


General, Performance Analyzer

In our continuing series on KPI Monitoring & Diagnosis, today we’re going to dig into examining changes to click through rate (CTR), which is one of the more complicated changes as there are so many factors that might be involved.

As a reminder, this data doesn’t exist in a vacuum. It’s easiest to see this information in the context of other data in your account, which is why we suggest you use the Performance Analyzer found within Adalysis or Data Studio reports to see how these metrics are interrelated. You can see how these reports are stories or get a copy of the Data Studio report here.


(Click image to see the full details)

Usually, CTR changes come from one of these key areas:

  • Total data consistency
  • Ad changes
    • Ad types
    • Ad testing
    • Ad rotation
  • Organizational changes
    • Ad group organization
    • Campaign settings
  • Impression changes
    • Bidding
    • Quality Score
    • Targeting changes
    • Budget
  • Match type usage
    • Duplicate keywords/search terms

These changes can often be interwoven, and you need to follow the cascading effects of decisions. For example, we saw an account that took a nosedive in CTR and conversion rates due to this chain of events:

  • User turned on enhanced CPC bidding
  • Google automatically changes the ad rotation to ‘optimize’ if you use any smart bidding options
  • In the campaign’s top impression ad group, Google started showing the 2nd worst CTR and worse converting ad the most

The apparent cause of the problem was the top performing ads were showing less often; the root cause was trying eCPC bidding. It’s these cascading effects that can make diagnosing CTR changes difficult at times.

To examine these CTR change possibilities, we’re going to look into each of these areas, so you have a checklist of the types of things to look for in determining why your CTRs are changing over time.

Total Data Consistency

It’s worth nothing that the most data you have, the more stables CTRs become unless there’s a change. If you get 100 impressions a month, a single click can change your CTRs quite dramatically. This is why it’s common to see some ad groups have massive CTR swings month over month and it’s only due to a few click differences.

Once you have a few thousand impressions, or millions of impressions, per month, then your data becomes very stable. So always keep in mind how much data you’re examining each month and the level you’re reviewing (ad group, campaign, groups of campaigns) to ensure you’re not chasing a few clicks as you examine the data.

How Ads affect CTR

Ad Types

The ad types you use can affect CTR. RSAs usually have higher CTRs than ETAs (and lower conversion rates). As you know the message in ETAs, their data is more stable than RSAs month over month. It’s not uncommon to see an ad group or campaign that only uses RSAs to have some wide swings in CTR and conversion rates.

Ad Testing

As you introduce new ads, your CTRs will naturally change as the new ads will now be served in place of the old ads for some impressions.

Ad Rotation

When you use ‘rotate’ as your ad serving option, your CTRs are generally stable and changes in CTRs come from changes to the ads (or targeting and other areas we’ll get to) and not due to the other ads in the ad groups taking impressions from your top ads.

When you use ‘optimize’ it’s common to see some wide swings in data on occasion as Google is often optimizing for CTR (over conversion rates) and the system can make mistakes in the ad serving. These mistakes can affect your CTRs.

For example, in this ad group, the ad with the lowest CTR (0.35% vs. 2.32%) has been served 42,428 times versus the higher CTR ads 27,875 impressions.


If nothing else in our diagnosis, from targeting to impression shares, has changed; then usually changes in CTR are directly due to different ads increasing and decreasing in impressions. This can be hard to spot as you need to dig deep into the data to find out that in a few high impression ad groups the ads with the most impressions changed over time. This doesn’t happen very often is you use rotate ad serving. It usually only occurs when you use optimize ad serving.

Organizational Changes

Campaign Settings

This should be super obvious, but in the interest of completeness, needs to be said. If you change your campaign settings, this can affect your CTR based upon the setting change.

For instance, if you change where your ads are served (locations), then you could have different CTRs in these new locations, and thus you’ll see a change in CTRs. If you were only on desktops and started to include mobile devices, then your CTRs will be different by device and directly affect your CTRs.

Organizational Changes

If you change anything about your organization, from campaigns to ad groups, expect to see CTR changes. For instance, if you move a keyword from one ad group to another one, then you’ll usually have a different ad in the new ad group, and thus a different CTR will be the result.

The most common thing that happens is you are examining your search terms to find new keywords with a pretty standard workflow:


In looking at your search term data, you add a few new keywords. If you add these search terms to more relevant ad groups (or create new ad groups) than from where the queries were showing, you should see an increase in CTRs.

Impression Changes

Top & Absolute Top Impression Shares

If your top and absolute top impression shares change, then you’ll see changes to your CTR. As this data is related to bidding, ad extensions, and quality scores, we’ve written a diagnosis article on this topic that you can see here: PPC & KPI Monitoring: How to Diagnose Lost Search Impression Share Rank & Top Impression Share Changes.

What this means is that any changes to bids, bid modifiers, quality score, and ad extensions can affect your CTRs.

Targeting Changes

If you make any changes to targeting, that can affect your CTRs:

  • Adding new keywords
  • Changing match types
  • Adding audiences
  • Removing audiences
  • Adding negative keywords
  • Pausing keywords
  • etc..

If you have a search term that has a very high CTR and a very poor conversion rate, then you’ll add a negative keyword to stop showing for that search term. The result of that negative keyword should be a lower CTR as you blocked a high CTR term, but an increase in conversion rates.


Budget can have some tricky effects on CTRs. If your budget is limited, which means you can’t serve ads in a campaign 100% of the time. What happens is that the keywords and ads that received traffic during one time frame can easily switch during the new time frame. The keywords and ads might not have changed CTRs, what did change was the frequency that they were displayed and the higher CTR keywords and ads could have increased or decreased in impressions.

If you raise your budget, then keywords that weren’t showing all the time might show more often. If those were low CTR words, that could lower your CTRs.

Match Type Usage

Your usage of match types can affect CTRs, especially if the search terms change over time.

For instance, if you use broad match, as your Quality Score goes up, you can show for a wider variety of search terms. These terms are usually less related than the initial terms, and thus can lower your CTR.


This is a bit of a complex topic, so we have an entire article on the phenomenon:  How Using Broad Match Can Lower Your CTR as Your Quality Score Increases.

These changes are almost always driven by changes in the search terms for which your ads were displayed. When you see significant changes in CTRs that aren’t from some of the previous factors, take a look at your search query changes, and see if they are changing over time.

Changes in How Match Types Function

We’ve seen Google change exact match, phrase match, and modified broad match quite a bit in the past year. This latest change has lead to a lot of duplicate search terms (search terms showing from multiple ad groups) and some volatility in CTRs and conversion rates for quite a few advertisers. You can read more about the latest changes here: How to Work with the Latest Google Ads Match Type Changes.


Changes in click through rates might not be bad. If you add a negative keyword to high CTR, but poorly performing search term, and your conversion rate goes up while your CTR goes down, that is a net positive for the account.

What you are usually looking for is times that your conversion rate didn’t change much (or dropped, but that’s another article) and your CTR went down. That result is often less clicks, and if your impressions didn’t change, then fewer conversions.

The primary time to dig into CTR changes is when your total volume of clicks is dropping, and thus you see fewer conversions for your account. The other time is when you see your Quality Scores dropping. As CTR is a significant factor in Quality Score, ensuring you maintain a healthy CTR also help maintain good Quality Scores.

When diagnosing changes to CTRs, start with the obvious:

  • Targeting changes
  • New ads
  • Budget changes
  • Organizational changes

You usually remember those types of changes, so it can be easy to check if any of those changes were made in your account. If that’s not the issue, then you need to look into changes to your search terms (which is always an insightful diagnosis) and impressions for your ads.

Once you have diagnosed why your CTRs changed, then you can put any new strategies or changes in place to improve then where improvement is needed.

Just remember, CTR is just one metric, and seeing it decline may not be a bad thing if you see your conversion rate and total conversions increase.

As a reminder, we’ll keep this series going for several more articles. To stay informed of this series and other articles we’re producing, you can subscribe here.

We hope you’re enjoying this lengthy and in-depth series.

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One Comment

  • debora M

    I’ve learned something good from this blog. The information provided is great and helpful. Thanks for sharing.

  • Leave a comment

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