How to identify First-Click attribution using GA4 and BigQuery

First-click attribution does not live in standard reports

The question “how did you find out about our brand?” never disappeared.
It simply moved from forms to raw data.

If you want to answer it today, GA4 default reports are not enough.

The real answer lives in the BigQuery export.

The dimensions that tell the story

To build a first-click attribution model using GA4 + BigQuery, a few dimensions are critical:

user_pseudo_id

The device identifier.
The user’s unique signature in the GA4 ecosystem.

ga_session_id

The Google Analytics session ID.
It groups events within the same visit.

ga_session_idx

The session index.

It answers:

Is this the device’s first, second, or tenth visit?

This field separates discovery from returning behavior.

step

An ordering of events within a session, usually calculated as:

ROW_NUMBER() OVER (PARTITION BY ga_session_id ORDER BY event_timestamp)

It lets you read the journey page by page.

Where first-click really happens

First-click attribution can be identified when:

• ga_session_idx = 1 → the device’s first-ever visit
• step = 1 → the first page of that session

📍 This is the true origin of the relationship with the brand.

Everything else comes after.

Why this matters for SEO and marketing

This is where SEO becomes visible.

SEO rarely closes the deal.
But it often opens the door.

Without this model:

• SEO looks like it doesn’t deliver value
• awareness campaigns seem inefficient
• decisions are driven only by the end of the funnel

With this model:

• discovery becomes visible
• each channel’s role is clearer
• growth stops being a mystery

Analytics is not just conversion — it’s narrative

First-click attribution allows you to reconstruct the user story:

1. how they arrived
2. where they entered
3. who introduced the brand

Without it, you measure outcomes.
With it, you understand growth.

Good data. Happy clicks.

#ga4 #bigquery #marketinganalytics #attributionmodeling