Vanadium dioxide (VO2) is a phase-change material between the monoclinic (M) and rutile (R) phases of the lattice with an insulator-to-metal transition (IMT) at 68 ◦C. This transition offers massive modifications in its optical properties, such as the refractive index, extinction coefficient, reflectance, and transmittance. These features make VO2 highly attractive to the smart window technology, as it enables the utilization of solar heat and transparency under dynamic control to maximize energy savings. In this study, VO2 thin films were modeled to investigate the phase-controlled optical characteristics of such materials in terms of the refractive index (n), the extinction coefficient (k), and the transmittance. The coefficients were determined using the dielectric function to assess the light behavior in each phase. The transmittance was also considered to depend on the film thickness. The results showed that the metallic phase has a higher reflectance and lower transmittance than the semiconducting phase. It was observed that there was a minor increase in transmittance with increasing thickness, and hence, film geometry can be applied in fine-tuning the optical performance. Such findings can be used to design the VO2-based devices to optimize them, particularly with regard to smart windows, among other photonic uses.