In this work, laminar flow through a slit between parallel plates has been analyzed. The flow rate based formulation for such flows, with slip and yield, has been established. The method has been verified for both the Bingham and Herschel-Bulkley fluids. Then, the method has been applied to the Herschel-Bulkley model with slip, and the Bingham-Papanastasiou and Windhab models. Moreover, the method has calculated velocity of the Carreau fluid with slip and yield, which has been found to be consistent with the velocity by the conventional method.