We present a newly developed code, QUINDI, to address the numerical challenge of calculating the radiation spectra from electron bunches in bending magnet systems. This code provides a better tool for designing diagnostic systems such as bunch length monitors in magnetic chicanes. The program calculates emission on a first principle basis, combining the dominant emission processes in a bending magnet system - edge and synchrotron radiation. The core algorithm is based on the Lienard-Wiechert potential and utilizes parallel computer architecture to cover complete electron beam distributions with a high resolution spatial grid. The program models the coherence level of the emitted radiation from the electron bunch, focusing on long frequency components.