Change-Address Detection

Change-address detection is the heuristic that identifies which output of a transaction returns unspent value to the sender rather than paying a counterparty.

In a UTXO transaction, inputs rarely match the payment amount exactly, so one output typically returns the remainder — the change — to an address the sender controls. Change-address detection uses signals like a freshly created address, matching script type, or round-number payment outputs to pick that output out. Correctly identifying change lets a clustering heuristic follow an entity forward across new addresses it never reused, dramatically widening a cluster. It is weaker than common-input ownership and easily confused by wallet coin-selection quirks, so systems assign it lower weight and reflect that in attribution confidence.