Sub ID (Affiliate Tracking)

A sub ID is a custom parameter an affiliate appends to a tracking link so the affiliate network or tracker can report back exactly which ad, placement, or traffic source produced each click and conversion. Instead of seeing one lump conversion count for a campaign, the buyer sees it broken out by whatever they encoded into the sub ID.

How sub IDs work#

A tracking link typically looks like trk.example.com/click?campaign=123&s1=taboola_us_ad4. That s1 value is the sub ID, and most trackers and networks support several slots (s1 through s5, or named parameters) so a buyer can encode more than one dimension per click. The click ID that comes back on the postback carries the sub ID value with it, which is what lets the buyer join a conversion back to the exact row it came from.

Common sub ID slots#

• Placement or creative ID: which specific ad image or headline variant got the click
• Publisher or site ID: which site or app the impression served on
• Geo or device: country, OS, or device type at the moment of click
• Campaign or ad set: which network campaign structure the click rolled up to

A media buyer running the same offer across MGID and Revcontent at once will typically stack network name into one sub ID slot and creative variant into another, so a single conversion report can be pivoted by either dimension without re-running anything.

Why it matters for optimization#

Without sub IDs, a buyer only knows a campaign converted at some blended rate; with them, they can see that one placement is paying for the whole campaign's EPC while three others are burning spend for nothing. That's the entire basis for cutting losing angles and scaling winners, whether that's done inside the network's own dashboard or a third-party tracker.

A worked example#

Say a buyer runs the same affiliate offer across four ad placements on MGID, three creative variants each, twelve combinations in total. Without sub IDs, the network report shows one campaign-level conversion count. With sub IDs encoding placement in one slot and creative in another, the same report splits into twelve rows. If nine of those rows show zero conversions and three are carrying the entire campaign's return, that's an immediate, specific decision: kill the nine, raise budget on the three. The alternative, guessing which combination is working from a blended average, usually means either scaling something that was actually losing money or cutting something that was quietly profitable. Pulling up the actual creative behind each sub ID on OpenAdLibrary is a fast way to confirm which specific ad a given sub ID row refers to when a network report only shows you an internal ID number.

Related terms#

Sub IDs work alongside a click ID and a postback URL: the sub ID identifies the source, the click ID identifies the individual click, and the postback is how the conversion gets reported back with both attached.