Abstract Seismic design codes generally specify empirical formulae to estimate the fundamental vibration periods of buildings. Currently, most building codes provide the same empirical formula to estimate the fundamental periods for steel plate shear walls and reinforced concrete shear walls. The work presented in this paper shows that the code formula predicts periods that are generally shorter than the periods obtained from a validated finite element analysis of a series of steel plate shear walls of different geometries. An improved simple formula for estimating the fundamental period of steel plate shear walls is developed by regression analysis of the period data obtained from analysis. In addition, the effectiveness of a simple shear–flexure cantilever formulation for determining fundamental periods and P – Δ effects of steel plate shear wall systems is presented. The effects of perforations in the infill plates and column base support conditions on fundamental periods are also explored.