In marketing, UTM parameters are tags you add to the end of a link to tell GA4 where a visit comes from: utm_source for the origin, utm_medium for the medium, utm_campaign for the campaign. GA4 reads these labels when the visit lands, then sorts the visit into the matching channel.

Think of the tag on a suitcase at the airport. The sorting belt reads the tag, then sends the suitcase to the right belt. If the tag is unreadable, the suitcase ends up at lost and found, which GA4 calls « (not set) » or « Unassigned ». UTM parameters serve anyone who sends visits from places other than Google Ads: a newsletter, a LinkedIn post, a Meta campaign, a QR code on a flyer.

What Are UTM Parameters Used For

The Analytics help center presents them as the way to identify the campaigns that send you traffic, by adding parameters to your destination URLs. They do three things.

  • Name an origin that GA4 cannot see. A QR code printed on a flyer has no website of origin to show: the tag gives it a name.
  • Compare your campaigns. Two posts, two newsletter subject lines, two visuals: utm_campaign and utm_content separate them in the same report.
  • Sort the visit into the right channel. The default channel group reads the source and the medium to decide if a visit comes from email, social networks or an AI assistant.

A UTM link is a normal address, followed by a question mark and name=value pairs joined by &:

https://example.com/offer/?utm_source=newsletter&utm_medium=email&utm_campaign=back_to_school

The Analytics help center lists the parameters that GA4 recognizes:

  • utm_source, the referrer: google, newsletter, linkedin.
  • utm_medium, the marketing medium: cpc, email, social.
  • utm_campaign, the name of the campaign, product or promo code.
  • utm_term and utm_content, the paid keyword and the creative, to separate two versions of the same campaign.
  • utm_id and utm_source_platform, the campaign ID and the platform that directs the traffic.

Google asks you to always use utm_source, utm_medium and utm_campaign. Two other parameters on its list, utm_creative_format and utm_marketing_tactic, do not appear in reports yet. The path of a tag then takes three steps.

  • The click: the person clicks, and the parameters travel in the address of the landing page.
  • The reading: the GA4 tag reads these parameters and attaches them to the session, as source, medium and campaign.
  • The sorting: the default channel group applies its rules. An email medium puts the visit in « Email », a social medium in « Organic Social », a referral medium in « Referral ».

These rules are published in the help page on the default channel group. Google states that they are not case sensitive and that you cannot edit them. A session that no rule recognizes goes to « Unassigned ».

A link carries three tags: when they are complete, the visit goes to its channel, which lights up; when the medium tag is missing, the visit falls into the bottom bin, Unassigned.

From July 18 to October 15, 2026, my site received 61 sessions from chatgpt.com. In the « Page location » dimension, the landing addresses of these visits carry ?utm_source=chatgpt.com: the source is written in the link, the medium is missing. GA4 filled in the rest. All 61 sessions show the medium ai-assistant and the campaign (ai-assistant), the values its rule assigns when the referrer is on its list of AI assistants, and all of them sit in the « AI Assistant » channel.

These sessions brought 5 of the 22 contact requests of the period. A link you tag yourself does not always get this help. Over the same 90 days, 12 sessions reached my site with utm_source=gmail and no medium. No rule recognizes this source alone, so GA4 put them in « Unassigned ».

To find the exact link of a visit, open the « Page location » dimension. The Analytics help center explains that GA4 removes UTM parameters from the « Landing page + query string » and « Page path + query string » dimensions. Full tracking of AI assistants is covered in the article on LLM traffic in GA4.

UTM Or GCLID: Two Tags, Two Uses

On Google Ads, the tag already exists. Auto-tagging adds a gclid parameter, the Google Click Identifier, to each click. The Google Ads help center settles the question: in GA4, auto-tagging is prioritized over manual tagging, due to the absence of an override option. UTM parameters added to a Google Ads ad do not change the source or the medium that GA4 shows.

They still have a role: utm_content and utm_term still feed the « Manual ad content » and « Manual term » dimensions (Analytics help). On the 12 client Google Ads accounts I have access to, auto-tagging is on everywhere, and two accounts still add UTM parameters to each click, through a final URL suffix or a tracking template. The GCLID remains the thread that ties the click to the conversion. The article on the GCLID, GBRAID and WBRAID shows how Google Ads adapts it to Apple's privacy rules.

On other platforms, the Analytics help center recommends dynamic parameters, such as {{campaign.name}} or {{site_source_name}}. The platform fills in the value on each click, and typing mistakes go away.

The Mistakes That Distort Your Channels

  • Case and spelling. For GA4, Meta and meta are two different values, and so are SpringSale and Spring_Sale. The Analytics help center advises using lowercase letters only. Channel rules ignore case: the visit lands in the right channel, but your source reports still split it into two rows.
  • The missing parameter. A missing parameter shows as « (not set) » in reports. A missing medium costs more: with a source that GA4 does not know, the visit goes to « Unassigned », like my 12 gmail sessions.
  • The made-up medium. utm_medium=newsletter or utm_medium=post match no rule. The values GA4 expects are written in its rules: email for email, social for social networks, referral for a referring site, cpc for paid traffic.

The site's UTM builder shows, before the link goes live, which GA4 channel it will land in, based on the rules Google publishes.

The Limits Of UTM Parameters

A UTM tag describes the link that was clicked, and only that link.

  • It travels with the link. A tagged address that gets copied keeps its tag. If a subscriber forwards your newsletter to a colleague, the colleague's visit also counts as a newsletter visit.
  • Anyone can read it. The parameters show in the address bar: an internal campaign name or a promo code is visible to everyone.
  • It stops at arrival. The tag says where the visit comes from. What the visitor does next, GA4 measures with its events, described in the guide What is GA4.

The Three Most Searched Questions

What are UTM parameters in a link? They are tags you add after a question mark at the end of a normal link, so that GA4 knows where the visit comes from. The link leads to the same page; only the tag changes what your reports show. Google asks you to always fill in the same three: the source, the medium and the campaign.

Where can I see UTM parameters in Google Analytics? In « Reports », open « Acquisition », then « Traffic acquisition », and choose the « Session source/medium » or « Session campaign » dimension. To read the full address with its parameters, use the « Page location » dimension: the landing page dimensions remove UTM parameters.

Do I need UTM parameters on Google Ads? For the source and the medium in GA4, auto-tagging is enough: its GCLID takes priority over UTM parameters, and the Google Ads help center says so clearly. Keep it on, and keep utm_content or utm_term for cases where another tool, a CRM for example, reads them. UTM parameters matter most on Meta, LinkedIn, email and printed material.

Before your next newsletter or sponsored post, write your link in the UTM builder and check which channel it lands in. If your reports already show « Unassigned » or « (not set) », the fix belongs with the rest of your measurement, in a Google Tag Manager and GA4 engagement.