Most online businesses operate across multiple hostnames. Your conversion goals -- signups, upgrades, purchases -- often happen on a different subdomain than where the visitor first arrived.

Understanding Domains, Subdomains, and Hostnames

Domain: The core identity of a URL. In www.example.com, the domain is example.com.

Subdomain: Used to organize different sections of a website. Examples: app.example.com, blog.example.com.

How a Visitor Journey Works Across Subdomains

When a visitor arrives at your site through a referral link, your analytics tracking script records the referral or UTM values. As the visitor navigates to a subdomain, the tracking script maintains session continuity as long as the same script is installed on both. Any conversions on the subdomain get attributed back to the original referral source.

Setting Up Cross-Subdomain Tracking

Install Tracking on All Subdomains

Most analytics tools handle subdomain tracking automatically when you register your main domain. Simply ensure the same tracking script is included on every subdomain.

Define Your Conversion Goals

Decide which actions to track as goals: product signups, subscription upgrades, newsletter subscriptions, or purchases.

Use Your Dashboard Effectively

Filter your analytics dashboard by the conversion goal and optionally by referral source. The data is hostname-agnostic by default.

Practical Example: Tracking SaaS Signups

Step 1: Install the same tracking script on all three hostnames. Step 2: Create a pageview goal for your signup completion page. Step 3: The tracking script records the full journey across subdomains as a single session. Step 4: Filter your dashboard by the signup goal to see conversion rates and top converting sources. Step 5: Use funnel visualization to track step-by-step progression.

Cross-Domain Tracking Considerations

Privacy-focused analytics tools typically do not maintain session continuity across entirely different domains, as this would require user profiling. For cross-domain scenarios, tracking domain exits as outbound link clicks is often the better approach.

Common Mistakes to Avoid

Creating separate accounts for each subdomain. A single setup covers everything.
Ignoring unexpected hostnames. Use hostname filtering to allow only your legitimate domains.
Confusing combined dashboards with continuous sessions. Sessions are only continuous across subdomains sharing the same tracking script.