In this paper, a method is given for defining the initial conditions in the switching circuits. In these circuits, peak currents/voltages (Dirac impulses) occur especially during switching instants. Therefore, the initial conditions of the system variables in t=0(+) (after switching) must be defined for time-domain analysis of the switching circuits. Normally, the initial conditions of the system variables in t=0(-) (before switching) are accepted as initial values of the system and used for the time-domain solution. But, sometimes in the switching circuits, the derivative components of the sources can be seen in the system equations when the switches change their states. It means that there are peak currents/voltages in the system. In this case, using the initial conditions in t=0(-) leads to incorrect solutions in the system analysis. Therefore, the initial conditions in t=0(+) must be calculated by the initial conditions in t=0(-). These values can be used in the solving of the system equations.