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We present a simple and accurate method for obtaining modal characteristics of highly lossy waveguides. The method requires locating the positions of Lorentzian peaks for both real and imaginary parts of the propagation constants. As compared to the method calculating half width at half maximum (HWHM) of Lorentzian peaks, the present method gives much more accurate results and works even in the cases where the former fails. The method is simple to implement and converges very fast. The applicability of the method is demonstrated by taking examples of surface plasmon resonance based planar waveguide structures.