The power-flow equation is employed to calculate bandwidth of step-index plastic optical fibers (POFs) for different launch conditions. The outcome specifies bandwidth as a function of the mean input angle and width of the launch-beam distribution. For small distribution widths, bandwidth is shown to decrease with increasing mean input angle of the launch-beam distribution. For large distribution widths, bandwidth becomes independent of the launch angle. Launch-beam distribution, mode-dependent attenuation, and mode dispersion and coupling in POFs strongly influence the bandwidth of data transmission systems.