Sway analyses of reinforced concrete buildings generally are carried out with computer programs. However, as the number of iterative solutions increase, the process may become tedious. This paper proposes a simple analytical method to evaluate sway of dual buildings subject to various types of lateral loads. The proposed method is based on the continuum model. Story drift limited by building codes can be controlled by the proposed method. Likewise, design engineers can use the simple analytical expressions to calculate the stability index, which includes sway terms at each story level. Stability index equation without sway terms is obtained by using the developed analytical expressions. Use of the equation, which is free of sway terms, is quite simple. Additionally, by using the proposed method, shear wall-frame interaction can be modeled simply. Thus, moment at the base of shear walls can be determined by using this model. Copyright (c) 2012 John Wiley & Sons, Ltd.