This paper presents a new formulation for the synthesis of planar six-bar linkages with only rotary joints showing two dwells in each cycle of the input crank. The formulation combines the concepts of instantaneous kinematics and optimisation to produce a simple, one-step synthesis method. The method is illustrated with a numerical example, where it is seen to produce better results in terms of accuracy and computational efficiency with respect to reported works. © 2009 Springer-Verlag Berlin Heidelberg.