Provided is a method of exactly calculating the delay of a gate in a digital integrated circuit (IC) that drives a capacitive load and a noise current source based on a crosstalk effect due to capacitive coupling between adjacent conductive lines, the method calculates the delay of the gate by using an output waveform that sums an output waveform of a linear time-varying output resistance model generated by using a gate output resistance library generated by using input and output voltage values of the digital IC and an output waveform of a modified Thevenin equivalent model of the gate.