Definition
Sub-ID tracking is a system that allows affiliates to add custom parameters, typically called sub1 through sub5, to their tracking links. These parameters pass through the entire click-to-conversion flow and show up in reports, letting both the affiliate and the program manager see exactly which traffic source, campaign, or creative produced each conversion.
How it works
An affiliate promoting your product across multiple channels might structure their links like this: yoursite.com/?ref=partner123&sub1=youtube&sub2=review_video&sub3=description_link. The sub1 identifies the channel, sub2 names the specific content, and sub3 marks the link placement. When a conversion happens, all three sub-IDs are recorded alongside the click and sale data.
The affiliate can then filter their reports to see that YouTube review videos convert at 4% while newsletter links convert at 1.5%. They double down on what works. On your side, you can see which types of content from each affiliate produce the best results, helping you decide where to focus co-marketing efforts.
Most tracking platforms support five sub-ID fields, but even using just one or two consistently makes a significant difference in your ability to optimize.
Why it matters
Without sub-IDs, you know that Affiliate A sent 500 clicks and generated 20 sales. With sub-IDs, you know those 20 sales came from their Instagram stories (12), their blog sidebar (5), and their email newsletter (3). That granularity changes the conversation entirely.
For program managers, sub-ID data reveals which promotional strategies actually work across your affiliate base. If you notice that video reviews consistently outperform banner ads across multiple affiliates, you can create better video assets and share that insight with your partners. You move from guessing to optimizing.
Trcker tip
Trcker passes sub-ID values through the entire conversion flow and displays them in your reporting dashboard, so both you and your affiliates can drill into performance by campaign, source, and placement.