A procedure for estimating the peak response of SDOF systems equipped with passive supplemental dampers using code-defined uniform hazard spectra is presented. The proposed procedure makes use of an improved equivalent linearization method that unifies the treatment of supplemental hysteretic and viscous-viscoelastic damping and can be readily implemented in a computer script. Nonlinear time-history analyses demonstrated that the proposed method makes significantly more reliable predictions than other common equivalent linearization methods for systems with supplemental dampers. Using the proposed procedure, performance spectra, which are plots of normalized response of SDOF systems with dampers, can be generated for practical performance-based design. To obtain a more complete description of the system performance, a simplified method for estimating the residual drift is also verified using results of extensive nonlinear time-history analyses. Copyright © 2012 John Wiley & Sons, Ltd.