We present simple and accurate analysis of coupling characteristics of identical single-mode graded index fiber directional couplers. Our analysis is based on the recently developed simple series expression for the fundamental mode of such a fiber involving Chebyshev technique. Analytical expressions of the relevant parameters are presented and the concerned calculations are executable with much less computations. With examples of step and parabolic index fiber directional couplers we show that our estimations match excellently with the exact results.