Best practices when changing attribution model in Google Ads

Get the most out of moving beyond last-click in Google Ads.

After you change your attribution model for a conversion type in your Google Ads account, follow the best practices in this article.

In this article:

Changes to expect in Google Ads

After changing your attribution model, you may notice changes to the reporting in your Campaigns tab.

  • Fractional Credit: Credit for a given conversion is distributed between contributing search ad clicks, according to your selected attribution model. As a result, you’ll see decimals in your Conversions column for the first time.

    Example: You select a linear model. A user follows the path generic keyword 1 > generic keyword 2 and then converts. In this case, each keyword will display 0.5 in the Conversions column from that conversion.
  • Time Lag: Google Ads reports conversions according to the date of the ad interaction. Since a non-last click attribution model shares conversion credit between multiple interactions, each of which happened at a different point in time, the time lag associated with your Campaigns reporting may increase. As a result, you may see a temporary, slight dip in conversions for very recent days after changing your attribution model.

    To understand how Time Lag impacts your business reporting, review the Time Lag report under Tools > Search Attribution > Time Lag. We recommend that you wait to evaluate performance until the average time lag reported for your accounts has passed.

Why you should change your bids and targets

If you change your Google Ads attribution model, you should update your bids and targets for each conversion included in the Conversions column. Otherwise, the change in conversion attribution may result in over/under bidding.

If you only use manual bidding, performance will not be impacted (positively or negatively) until you begin to optimize based on the new data. However, changing targets is especially important if you use Smart Bidding, as illustrated by Example 1, below.

Example 1

You use Smart Bidding. You change to a Data-driven model for your conversion action. You have two campaigns with the following last-click performance in the Conversions column over the last two weeks:

  • Brand (lower-funnel) campaign: $5 CPA, 200 conversions
  • Generic (upper-funnel) campaign: $20 CPA, 50 conversions

Because you use Smart Bidding, the targets above are also the targets used in bidding. 

Now, let's say that you look at the Conversions (current model) column, which reflects historical Data-driven attribution performance, and observe the following:

  • Brand (lower-funnel) campaign: $6.67 CPA, 150 conversions
  • Generic (upper-funnel) campaign: $10 CPA, 100 conversions

If you were to switch from the Last click to the Data-driven model while leaving CPA targets at the original $5 and $20, the changes in conversion rates would imply a set of bid changes that would underbid on the Brand campaign and overbid on the Generic Display campaign.

Calculate adjustments to your bids and targets

To view performance for your conversion action according to your newly selected attribution model, add the Conversions (current model) and Cost/Conv. (current model) columns to your reports. Learn how to add columns.

Compare these columns to the Conversions and Cost/conv. columns to see the change across models. Set your new target CPAs at the campaign level based on Conversions (current model) and Cost/Conv.(current model) performance. Exclude the most recent 14 days from your analysis to avoid the effect of time lag.

Example 2

You change the attribution model for your conversion action on September 1. Because you should exclude the last 14 days of data (August 18-31) from your analysis, you use the data from August 4-17 to help you calculate your tCPA adjustments.


Campaign Cost Conversions Cost/conv Conversions (current model) Cost/conv (current model) tCPA adjustment
Generic 1 250€ 200 1.25€ 280 0.89€ +29%
Generic 2 500€ 600  0.83€ 520 0.96€ +16%

For the Generic 1 campaign, there is a 0.36€ decrease in cost per conversion. To account for this decrease, you should adjust your tCPA down 29% (0.36/1.25=0.29).

For the Generic 2 campaign, there is a 0.13€ increase in cost per conversion. To account for this increase, you should adjust your tCPA up 16% (0.13/0.83=0.16).

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