SubID

A SubID is a custom value an affiliate appends to a tracking link to identify where a click came from — a specific page, campaign, placement or keyword. It passes through the conversion data so affiliates can optimise by source, and is essential for serious campaign analysis.

A SubID is an extra parameter an affiliate appends to a tracking link to label where a click came from, which passes through untouched and appears back in the affiliate's reporting. It lets a single affiliate account segment performance by page, placement, campaign, keyword, or audience without needing separate links from the network. The network stores whatever value is supplied and reflects it against any resulting conversion.

Because the affiliate defines the value, SubIDs are flexible: one slot might hold a page slug, another a traffic source, another an ad creative ID. Many networks support multiple SubID fields (often named subid, s1 through s5, or similar), letting affiliates build a small taxonomy that flows all the way to the conversion report. This turns an opaque lump of clicks into data an affiliate can optimize against.

The practical payoff is knowing which content and channels actually earn, so budget and effort shift toward the placements that convert and away from those that only generate clicks. Advertisers benefit indirectly, since affiliates who can see granular performance tend to send higher-quality traffic. Without SubIDs, an affiliate promoting across dozens of pages sees only a single combined number and cannot tell winners from losers.

Pitfalls include exceeding character or field limits, passing personally identifiable information (which violates most network terms and privacy law), and inconsistent naming that makes reports impossible to aggregate later. Values can also be truncated or dropped if links are shortened or rewritten, so affiliates should test that SubIDs survive the full click path before relying on them for decisions.