Microsoft Ads Auto-Tagging Rewrites Your UTMs

There are two auto-tagging checkboxes, and most people know one

Ask a marketer what auto-tagging does and you'll get the Google answer: it bolts a click ID onto your URLs. gclid on Google, msclkid on Microsoft, job done.

That answer is half right on Microsoft and the missing half is the expensive one. Microsoft Advertising has two separate account-level settings sitting in the same place under Campaigns, Settings, Account level options:

• Add Microsoft Click ID (MSCLKID) to URLs to allow conversion tracking. This is the gclid equivalent, it feeds UET conversion tracking, and per Microsoft's docs it's "enabled by default."
• Add UTM tags to my destination URLs. This one writes actual utm_ parameters onto your landing page URLs. Google Ads has no equivalent.

Nobody imports that second one into their mental model, because Google never taught them it could exist.

What it writes

Five tags, and one of them is a landmine:

Tag	Microsoft sets it to
utm_source	Bing
utm_medium	cpc
utm_campaign	The campaign
utm_content	The ad group
utm_term	The keyword (or Shopping product group)

Read that fourth row again. Most teams use utm_content for the creative variant, the thing you're A/B testing. Microsoft uses it for the ad group. So if you turn this on, your Bing rows mean something structurally different from every other channel in the same report, and no error appears anywhere to tell you. Our naming conventions guide exists for exactly this class of problem, and this is the rare case where the platform breaks your convention rather than a colleague.

(Small thing worth banking: Microsoft's own doc says utm_source is set to "Bing" in the table and shows utm_source=bing in the example directly below it. Doesn't matter for channel assignment, because Google's documentation states plainly that "channel definitions aren't case sensitive." It does matter for your report rows, where Bing and bing sit on separate lines.)

Replace, or preserve, and the line in the fine print

You get two options: wipe existing tags and use Microsoft's, or keep yours and let Microsoft fill the gaps.

Then Microsoft adds a Note that most guides skip entirely. That choice "checks UTMs in the tracking template." Manual UTMs living in your final URL or final URL suffix aren't checked, so running both "can produce UTM duplication in some circumstances."

Which is to say the preserve option doesn't protect the place a lot of teams actually put their tags.

The truncation nobody writes about

This is my favourite line in the whole document. The tags "are added in the order shown below from top to bottom until the maximum length of the URL is reached."

Top to bottom. utm_term is last.

So on a long landing page URL, the keyword data is the first thing to fall off the end, quietly, on some URLs and not others. You'd read that as a keyword-level reporting gap and go hunting through the ads platform. It's a string length problem.

You can't check any of this in the interface

Microsoft is upfront here and it still catches people. "Auto-tags are added when the ads are displayed... you will not see your landing page URL updated with the new tags."

The URL in your account isn't what gets served. Click a live ad, look at what lands, and read the address bar. That's the only honest verification, and it takes about thirty seconds.

One more constraint buried in the same notes: auto-tagging only works if your site tolerates arbitrary URL parameters. If yours strips unknown ones, this silently does nothing.

What's changing on September 2, and how much to trust it

Right now every Microsoft campaign type gets the same bing / cpc treatment, so Audience, Shopping and Performance Max all collapse into Paid Search in GA4. Trade press from June (PPC Land, Search Engine Roundtable, PPC News Feed) reports that Microsoft is splitting the values by campaign type effective September 2, 2026, with msads as the source for several types and Performance Max moving to a cross-network medium.

I'm not going to hand you the full value table, and here's why. Microsoft's own auto-tagging documentation was updated on July 27, five weeks after that announcement, and it still documents only the single old value set. I found no Microsoft release note. The trade reports also don't agree with each other on the exact medium string.

So treat it as likely and unconfirmed. If it lands as described, anyone whose GA4 channel grouping keys off utm_source=bing will watch a chunk of Microsoft spend change channel overnight. Worth knowing about, not worth rebuilding your channel mapping on a date no vendor doc confirms. Check a live ad in September.

If you want the version of this fight where the platform is better documented and still awkward, Google Ads auto-tagging and UTMs covers running both without one erasing the other, and click IDs vs UTMs covers what msclkid and gclid are actually for. Microsoft's problem isn't that it's badly behaved. It's that it does more than you think it does.