A method of parametric estimation of the decrement of damping harmonic oscillations based on calculation of the phase difference on the carrier frequency of direct and reverse-time oscillation process is proposed. By incremental truncation of the process’ digital realization’s discrete Fourier transform, a characteristics is formed the slope of which depends on the decrement. Numerical experiments are carried out on mathematical modeling and spectral analysis of damped oscillations to verify the method and determine the limits of its applicability.