We present a discrete-time time-domain vector fitting al- gorithm, called TD-VFz, for rational function macromod- eling of port-to-port responses with discrete time-sampled data. The core routine involves a two-step pole refinement process based on a linear least-squares solve and an eigen- value problem. Applications in the macromodeling of prac- tical circuits demonstrate that TD-VFz exhibits fast com- putation, excellent accuracy, and robustness against noisy data. We also utilize an quasi-error bound unique to the discrete-time setting to facilitate the determination of ap- proximant model order.