The determination of the set (or window) of segments that are inductively coupled to a significant degree with a given segment plays a fundamental role in window-based techniques for the extraction of the susceptanceof interconnect structures. We present a measure that quantifies the degree of coupling between segments in a window, thereby paving the way for an adaptive scheme for determining the coupling window associated with each segment. This measure has the properties that: (i) it is well-correlated with the simulation error that is inherent in window-based susceptance extraction techniques, and (ii) it can be computed efficiently using incremental and computation reuse techniques. These properties are validated on numerical examples.