How to Fix GA4 UTM Casing Fragmentation (Uppercase vs Lowercase)

Google Analytics 4 processes incoming hit query strings verbatim. Because the database engine stores string tokens as exact byte values, utm_source=Facebook, utm_source=facebook, and utm_source=FACEBOOK are recorded as three completely different traffic sources.

Crucially, GA4's Default Channel Grouping rules evaluate regex patterns against source and medium dimensions. When a medium is tagged as utm_medium=CPC or utm_medium=Paid_Social, the uppercase characters fail GA4's default rule definitions, causing high-value ad traffic to be classified as Unassigned.

Follow these 4 steps to eliminate casing fragmentation and unify your GA4 reporting data:

1. 1

   Identify Fragmented Rows in GA4

   Navigate to Reports > Acquisition > Traffic Acquisition in Google Analytics 4 and set the primary dimension to Session source / medium. In the search filter bar, select Matches regex and enter (?i)facebook|google|linkedin|email to immediately isolate and tally all mixed-case duplicate entries.

2. 2

   Standardize Naming Conventions

   Enforce all-lowercase values across utm_source, utm_medium, and utm_campaign in team tracking spreadsheets and advertising platforms. Replace all spaces with hyphens or underscores to eliminate clumsy %20 encoding.

3. 3

   Automate URL Sanitization

   Use client-side enforcement to auto-lowercase URL query parameters prior to pushing ad links live. Additionally, configure edge middleware (e.g. Next.js Edge Middleware or Cloudflare Workers) to automatically intercept incoming capitalized UTM parameters and permanently redirect (HTTP 301) to normalized lowercase query strings.

4. 4

   Historical Data Note

   Google Analytics 4 does not retroactively rewrite or reprocess historic data; fixes apply only to newly collected sessions. To clean up historical reports, create a Custom Channel Group in GA4 Admin using case-insensitive regex or create calculated fields using LOWER(Session source / medium) in Looker Studio or BigQuery.

Select a solution below to sanitize URLs client-side or rewrite casing at the edge before GA4 tags execute:

export function sanitizeUtmUrl(rawUrl: string): string {
  const url = new URL(rawUrl);
  const keys = Array.from(url.searchParams.keys());
  keys.forEach((k) => {
    if (k.toLowerCase().startsWith("utm_")) {
      const v = url.searchParams.get(k) || "";
      url.searchParams.delete(k);
      url.searchParams.set(k.toLowerCase(), v.toLowerCase().trim().replace(/\s+/g, "-"));
    }
  });
  return url.toString();
}