The five parameters, and the three that really matter
utm_source identifies where the traffic comes from: the name of the platform or referring site. utm_medium identifies the type of channel: cost per click, email, affiliate, social media. utm_campaign names the marketing campaign.
Those three are essential. The other two are for fine-tuning, not for structure: utm_content tells two creatives apart, and utm_term is inherited from paid keywords.
The most common structural mistake is confusing source and medium: putting “facebook” as the medium rather than the source breaks every grouping by channel type, and makes it impossible to compare platforms.
The mistakes that make a report unusable
Capitalization. Values are case-sensitive in most tools: Google and google produce two separate rows. An all-lowercase convention, with no exceptions, saves hours of cleanup.
Spaces and accents. They turn into unreadable strings in reports. Hyphens and plain characters are all you need.
No written convention. Without a shared reference document, everyone invents their own naming. After a few months, the data can no longer be aggregated, and the problem is retroactive: you cannot rewrite history.
Tagging internal links. Adding UTMs to links within the site breaks the current session and reassigns the visitor to a new source. It is one of the most common causes of inconsistent numbers.
Leaving some links untagged. A partially tagged campaign produces traffic classified as direct, which silently undervalues the channel concerned.
UTMs and attribution: what they leave unsolved
UTMs describe the last entry point, not the journey. A visitor who discovers a brand through a social ad, comes back three days later through a branded search, then buys, will be attributed to search. The ad that sparked the interest appears nowhere.
That is why a dashboard based only on UTMs systematically undervalues discovery channels in favor of closing channels.
UTMs are still essential: they are the most reliable and least expensive building block of the measurement setup. They are simply not enough on their own to allocate a budget.
Frequently asked questions
What are UTM parameters for?
To identify where a visit came from in analytics tools. Without them, some of your paid traffic and email campaign visits end up classified as direct traffic, which makes it impossible to evaluate channels.
Which UTM parameters are required?
utm_source, utm_medium, and utm_campaign structure the analysis and should be used every time. utm_content and utm_term are optional and are for fine-tuning.
Should you put UTMs on your site's internal links?
No. Tagging an internal link breaks the current session and reassigns the visitor to a new source, which skews both the origin of the visit and the session count.
Why are my UTMs missing from my reports?
The usual causes: a redirect that strips the parameters, case differences creating separate rows, or declined consent preventing measurement. Checking the URL actually reached after the redirect solves most cases.