We have shown that the S1 (HOMO→ LUMO) DCT can be predicted by a novel metric, η, that computes the average similarity between a donor (acceptor) molecule's HOMO (LUMO) and that of the corresponding orbital in the D-A complex. We find that η exhibits a positive linear correlation with S1 DCT for a set of 31 D-A pairs. In choosing molecular geometries to compute η, we find that in comparing orbitals between isolated donor and acceptor molecules and their corresponding D-A complexes, one should use the same molecular geometries in the isolated molecules as in the D-A complex. Alternatively, experimental crystal structure data for the D-A complex can be used instead of optimized D-A dimer geometries. This allows flexibility in input data for inclusion in high-throughput screening and machine learning protocols. Lastly, we compare two methods for determining DCT, NBO and TDM analysis, and find that TDM is more reliable due to its ability to treat electron delocalization. Future work will aim to generalize the η metric to characterize the DCT of other electronic states, with the goal of uncovering further orbital structurefunction relationships.