We compute exciton binding energies and fine‑structure splittings in CdSe nanoplatelets with two zincblende geometries and one wurtzite geometry, finding that the wurtzite structure exhibits the largest bright‑bright splitting due to its intrinsic in‑plane anisotropy, while the zincblende structures show smaller but finite splittings arising from atomistic symmetry breaking at edges and corners. These results are obtained using a theoretical framework that we developed, which combines DFT single‑particle states with screened configuration interaction, a quasi‑2D dielectric screening model, and an efficient Coulomb‑cutoff scheme that eliminates periodic‑image interactions and enables accurate Coulomb and exchange integrals at low computational cost. This methodology provides a transferable and practical route for studying excitons in CdSe nanoplatelets and other quasi‑two‑dimensional nanomaterials.