GA4 Attribution: Models, Lookback Windows and Conversion Paths

What attribution means in GA4

Google's Get started with attribution page defines attribution as "the act of assigning credit for important user actions to different ads, clicks, and factors along the user's path to completing the action." The important actions are your key events: the events you marked as important in GA4, such as a form submission or a purchase. If you have not set those up yet, start with our GA4 basics guide.

An attribution model is the rule, or the data-driven algorithm, that decides how that credit is split between the touchpoints on the path. The model changes how credit is shared out between channels. It does not change how many key events happened.

The models GA4 offers today

Google lists three models in the Attribution reports:

• Data-driven. Credit is shared based on your own property's data for each key event. Google says the model uses machine learning to compare converting and non-converting paths, and takes into account things such as the time from the key event, device type, the number of ad interactions, the order of ad exposure and the type of creative. Each data-driven model is specific to the advertiser and to the key event, and Google notes that conversions can be reattributed for up to 7 days after the conversion.
• Paid and organic last click. This ignores direct traffic and gives 100% of the credit to the last channel the person clicked through (or, for YouTube, an engaged view) before converting. Google adds that this is the same model as last non-direct click. In Google's examples, Display > Social > Paid Search > Direct gives 100% to Paid Search.
• Google paid channels last click. This gives 100% of the credit to the last Google Ads channel clicked before converting. If there is no Google Ads click on the path, it falls back to paid and organic last click.

One rule applies to all three: Google says all attribution models exclude direct visits from receiving credit, unless the path to the key event consists entirely of direct visits. So a sale that came only from people typing your address in still shows as Direct, while on a path with an email click before the direct visit the credit goes to Email, not Direct.

With data-driven attribution you will also see decimals in the Key events and revenue columns. Google calls this fractional credit: on a path of two keywords, each keyword shows part of the key event, and the parts add up to 1.0.

The models that were retired

Older articles about GA4 still describe first click, linear, time decay and position-based models. Google's Select attribution settings page says these four are no longer available as of November 2023. Google's announcement of the change, dated April 6, 2023, explained that they were going away across Google Ads and GA4, and that data-driven, last click and external attribution would not be affected. If a tutorial tells you to pick position-based in GA4, it was written before that change.

For the Google Ads side of this change (which models conversion actions use, and what happened to actions that used the old ones), see our Google Ads conversion tracking guide.

The three attribution settings

You find the settings in Admin: under Data display, click Events, then Attribution settings (Google's newer help page on changing the model calls the item Key events attribution). Google says you need the Marketer role or above at property level to change them. There are three settings.

Reporting attribution model

This is the model your GA4 key event reports use, and the reports of any linked Firebase projects. Google says changing it applies to historical and future data, so last month's channel figures can shift the moment you save. The newer help page marks data-driven as recommended. Google also gives start dates: paid and organic data-driven attribution from November 1, 2021, and the rules-based models from June 14, 2021, so a date range before those shows partial data.

Channels that can receive credit

You choose between Paid and organic channels and Google paid channels. Paid and organic gives a cross-channel view that includes organic search, email, social and other sources. Google paid channels shows conversions from Google Ads. Google's notes on this setting matter if you advertise:

• It applies going forward and to all linked Google Ads accounts, and it may affect the conversions you use for bidding and reporting in Google Ads. Google says it may take a few days to show there.
• Paid and organic channels only applies to web conversions. App conversions always use Google paid channels.
• By default, Google Ads reports use Google paid attribution and GA4 reports use paid and organic attribution.

Key event lookback window

This sets how far back a touchpoint can be and still earn credit. It is covered in the next section.

Lookback windows

Google's example: with a 30-day window, key events on January 30 are attributed only to touchpoints from January 1 to 30. The options are:

• Acquisition key events (first_open and first_visit): 30 days by default, or 7 days.
• All other key events: 90 days by default, or 30 or 60 days.

The window applies to all models and all key event types, and Google notes that it also applies to session attribution. Unlike the model, a change to the lookback window only applies going forward. If your sales cycle is short and you want campaigns judged on recent touchpoints, a shorter window does that; if people take weeks to decide, the 90-day default keeps early touchpoints in view.

Which reports change, and which do not

This is where most confusion comes from. Google says the reporting model is reflected in key event reports and explorations that use event-scoped traffic dimensions such as Source, Medium, Campaign and Default channel group. User-scoped and session-scoped dimensions, such as Session source or First user medium, are not affected.

Google's page on scopes of traffic-source dimensions explains the prefixes: First user dimensions show where a user first came from and keep that value when they return (the User acquisition report), while Session dimensions get a new value with each session (the Traffic acquisition report). So if you switch from data-driven to last click and the Traffic acquisition report does not move, that is expected. Compare numbers within the same scope, and note which model was set when you report figures. How sessions get their source in the first place depends on clean tagging, which our UTM tracking links guide covers.

Model comparison and attribution paths

Both reports sit in the Advertising section of GA4, under Attribution.

Model comparison. Google's tutorial on attributing credit describes it as a way to see how different models impact the valuation of your marketing channels, for example paid and organic data-driven against paid and organic last click. It is the safe way to see what a model change would do before you change the property setting.

Key event attribution paths. Google's attribution paths report page says the report shows which channels initiate, assist and close key events. Some points from that page:

• Paths are split into early touchpoints (the first 25%), mid touchpoints (the middle 50%) and late touchpoints (the last 25%), and the chart shows how much credit each segment gets under the model you pick from the drop-down.
• The table lists paths with Key events, Purchase revenue, Days to key event and Touchpoints to key event, sorted by default by the paths with the most conversions.
• It shows paths up to 20 touchpoints long, and data from June 14, 2021 onwards.
• Only users who triggered a key event appear. A path with no key event is not in the report.
• You can switch the breakdown from Primary channel group to Source, Medium or Campaign, and add filters such as browser.

Days to key event is a useful number for a small business: it tells you how long people usually take to enquire, which helps you pick a lookback window and set expectations for a new campaign. For custom path analysis beyond these reports, see our GA4 explorations guide.

Which settings suit a small business

Google recommends data-driven as the reporting model, and for most sites it is a reasonable default because it is built from your own data. Three practical points:

• If you only want to know what your Google Ads spend produced, Google paid channels gives that view, but the rest of your marketing loses its credit in GA4 reports. Most businesses with organic search, email and social are better served by paid and organic.
• Change settings rarely, and write down when you did. A model change rewrites past figures; a lookback change only affects the future. Either way, a before/after comparison across the change date is not like for like.
• Expect GA4 and Google Ads to differ. Google notes that the two use different default channels for credit, and that different time zones in the two accounts can cause discrepancies. Our analytics reporting guide suggests what to put in a monthly report so those gaps do not cause confusion.

A checklist

• Key events set up for the actions that matter (enquiry, call click, purchase).
• Reporting attribution model checked in Admin, and its name noted in your reports.
• Channels that can receive credit set on purpose, knowing it also affects linked Google Ads accounts.
• Lookback windows matched to how long your customers take to decide.
• Model comparison report checked before changing the model.
• Attribution paths report reviewed for Days to key event and the channels that start journeys.
• Date of every settings change recorded.

FAQ

What is the default attribution model in GA4?

Google's help pages say GA4 uses the data-driven attribution model by default, and Google marks it as recommended. You can switch to paid and organic last click or Google paid channels last click in the attribution settings.

Can I still use first click or linear attribution in GA4?

No. Google says the first click, linear, time decay and position-based models are no longer available as of November 2023.

Does changing the attribution model change past data?

Yes. Google says a change to the reporting attribution model applies to historical and future data. A change to the lookback window only applies going forward.

Why does direct traffic get so little credit?

Google says all GA4 attribution models exclude direct visits from receiving credit unless the whole path to the key event is direct visits.

Why did my Traffic acquisition report not change when I switched models?

The reporting model only affects key event reports and explorations that use event-scoped traffic dimensions. Session-scoped dimensions such as Session source, used in Traffic acquisition, are not affected.

Why are there decimals in my key events?

With data-driven attribution, credit for one key event is shared between touchpoints, so each one can show a fraction. The fractions for a key event add up to 1.

Want analytics that show what your marketing really does? See our website development service and all our services, or email [email protected].