A fast and accurate method of determining path delay and phase advance and range error between any two satellites for L-band frequencies has been determined. The method takes into account the bending of the ray path due to refraction by both vertical and horizontal gradients as well as the effect of the geomagnetic field and the actual profile of the electron density and its gradients along the path. The method has been validated against both analytical and precise numerical calculations. Results are presented of first and higher order ionosphere errors and path displacements from the LOS for satellite to ground and satellite to satellite paths.