There is described a method of optimizing the design of an electronic device with respect to electromagnetic emissions based on frequency spreading. With the method, a designer can, for example, perform a transient simulation on the device only once, and then add frequency spreading with specific parameters by simulation. The resulting frequency spread signal can be observed. The designer can thus evaluate the reduction in electromagnetic emission level, and repeat this process by iteratively applying frequency spreading each time with specific parameters but without having to modify the schematic of the device and to perform another simulation of the device. The method according to this innovation is extremely rapid as the simulation of the design does not need to be repeated at each run of the frequency spreading simulation.