First user source vs session source in GA4: which channel brings customers?
GA4's first user source is where someone first found you; session source is the visit they bought on. How to compare them, and what each tells you.
In Google Analytics 4, first user source is where a person came from the first time GA4 saw them, and it never changes. Session source is where each visit came from. A signup or a sale belongs to both: the channel that first found the person, and the visit it happened on. Comparing the two shows which channels find customers that other channels then get the credit for.
The two in plain words
| First user source | Session source | |
|---|---|---|
| What it is | Where the person came from first | Where this visit came from |
| Changes when? | Never, for that person and browser | Every visit |
| Where GA4 shows it | The User acquisition report | The Traffic acquisition report |
| A sale counts under… | The channel that found the person | The channel of the visit they bought on |
Both skip direct visits when GA4 knows an earlier source: Google calls this "paid and organic channels last click". So someone who first came from X and later typed your address to buy still counts as X for that visit, not Direct.
An example
Someone sees your post on Reddit and visits. A week later they search your name on Google, come back and buy.
- First user source: reddit.com
- Session source of the buying visit: google
In the Traffic acquisition report the sale sits under Google, and Reddit gets nothing. In User acquisition it sits under Reddit. Neither is wrong: Reddit found the customer, and Google brought them back.
Compare them in GA4
In GA4, open Explore and start a Blank exploration (Free form).
Under Dimensions, add First user source and Session source. Under Metrics, add Event count.
Drag both dimensions to Rows and Event count to Values.
Add a filter: Event name exactly matches your signup or purchase event, such as sign_up or purchase.
Each row is now a path: first source, then the source of the visit with the event, and how many times it happened.
What to look for
| What you see | What it tells you |
|---|---|
| A source with many sales as first, few as session source | It finds people who buy later, often through another channel |
| Google or Direct with many sales from people found elsewhere | They bring people back; something else found them first |
| A source with the same counts in both | People find you and buy in the same visit from it |
| Many "(not set)" first sources | Those people first came before GA4 was on your site, or GA4 lost track |
Keep to the counts. They show which channels found and brought back the people who signed up; they don't say why someone bought.
Limits
- Per browser. GA4 knows a person by their browser (or your user ID, if you send one). Someone who switches device or clears cookies is a new person, with a new first source.
- Events, not people. Event count counts each signup or purchase, so one person who buys twice counts twice.
- Not the attribution reports. GA4's attribution reports, such as Model comparison, share each key event out between channels with a model, so they show parts like 1.3 sales. First user source and session source give whole counts.
Related
Sources
- Google: Scopes of traffic-source dimensions (checked Oct 17, 2026)
- Google: API dimensions and metrics (checked Oct 17, 2026)
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