UTM Source vs Medium: Which Value Goes Where, With Examples

Open the free UTM builderDownload the source and medium cheat sheet (PDF)

The difference in one sentence each

utm_source is who sent the visit. The platform, the list or the website the person clicked through from: facebook, instagram, newsletter, google, or the name of a partner's site.

utm_medium is the kind of link it was. An unpaid social post, a paid ad, an email, a text message, a link on another website: social, paid_social, email, sms, referral.

Google's help page on campaign URLs describes source as the referrer (its examples are google, newsletter4 and billboard) and medium as the marketing medium (cpc, banner, email). A quick test: if you could swap the platform without changing the medium, you have them the right way round. A paid ad on Facebook and a paid ad on Instagram share a medium (paid_social) and differ in source.

Why the medium matters more than it looks

In GA4, the source and medium pair is not just a label. It decides which channel the visit counts towards in the Traffic acquisition report, and most people read the channel view first. The rules are published on Google's default channel group page, and the ones that matter for tagged links are:

• Organic Social: the source matches Google's list of social sites, or the medium is social, social-network, social-media, sm, "social network" or "social media".
• Paid Social: the source matches a social site and the medium starts with paid, contains cp (such as cpc or cpm), or is ppc or retargeting.
• Paid Search: the source matches a search site and the medium follows the same paid pattern.
• Email: the source or medium is email (e-mail, e_mail and "e mail" also count).
• Referral: the medium is referral, app or link.
• SMS: the source or medium is exactly sms.
• Organic Search: the source is a search site, or the medium is exactly organic.

Two things follow. First, a medium Google does not list sends the visit to Unassigned, even when the source is perfect. Second, swapping the two values breaks the sorting: a link tagged source=social and medium=facebook matches neither rule, because "social" is not a social site and "facebook" is not a social medium, so it lands in Unassigned. Google also notes that channel definitions are not case sensitive, but the values in your reports are, so Facebook and facebook still show as two sources.

The pairs for common small-business links

The last two rows are judgement calls. The Business Profile pair keeps those visits inside Organic Search, where Google would have put them anyway, while the campaign tag still separates them; our guide to tracking your Google Business Profile explains the trade-off. The QR pair gives up a named channel so that every printed code is easy to find under Session source / medium; if you would rather see them in a channel, use medium=referral and accept that they mix with real referrals.

Four mix-ups that send visits to the wrong channel

1. The platform in the medium. medium=facebook with source=social. GA4 reads neither value as a social site or a social medium, so the visits fall into Unassigned. Swap them.
2. Paid and unpaid under one medium. Tagging both your Facebook posts and your Facebook ads as social puts ad clicks in Organic Social, which makes the ads look worse and the posts look better than they are. Ads get paid_social.
3. The campaign in the source. source=spring_sale tells you nothing about where the person was when they clicked. The offer belongs in utm_campaign; the source stays facebook or newsletter, so the same offer can be compared across channels.
4. A different word every time. social one week, social_media the next, Social the week after. GA4 accepts several spellings for the Organic Social channel, so the channel total looks right, but the source / medium report splits into rows that never add up. Pick one.

A useful check once a month: open Traffic acquisition with Session source / medium as the first column and scan for any medium that is not on your list. Every odd one is a link someone built by hand. Find it, rebuild it with the right pair and replace it where it is posted.

Step by step: choosing the pair for any new link

1. Name the sender

Who or what does the person click through from? That is the source. Use the platform's plain lowercase name and the same one every time.

2. Name the type of link

Did you pay for the click? Is it an email, a text, a link on someone else's site, or an unpaid post? That decides the medium.

3. Take the medium from GA4's list

social, paid_social, email, cpc, sms or referral cover nearly everything. Keep the list in your naming convention so nobody invents a new one.

4. Build the link

In the free UTM builder, the presets fill in both values for Google Ads, Google Business Profile, Facebook post, Facebook ad, Instagram, Instagram ad, LinkedIn, Email newsletter and QR code. Add the campaign name, copy, and open the link once to check the tags are still in the address bar after the page loads. The full routine is in our guide to creating UTM links.

Later, when you want to know which source brought paying customers rather than visits, that is a job for whatever receives the enquiry. On paid plans, Fynl saves the source, medium and campaign on each lead that comes in through its forms, website pages or chat, and its Reports page counts leads and won jobs per source.

The UTM builder sits with the QR code generator, the calculators and the other no-cost tools on our free tools page.

Questions people also ask

Sources

• Google Analytics Help — URL builders: Collect campaign data with custom URLs
• Google Analytics Help — Default channel group