In this paper, we present a fast and accurate delay estimation method for buffered interconnects. The interconnect wire is modeled by the transmission line model which is more accurate and efficient than lumped circuit model. For the interconnect wire, we specify the wire shape to be of the form f(x)=ae-bx. Note that if we let b=0, our work is reduced to uniform wire case. By using the first three poles in the transfer function, we derive analytical expressions for calculating delay at any threshold voltage under a finite ramp input. The expressions involved in calculating coefficients in the transfer function are also analytical. We use k-factor equations to estimate delays for buffers. Since the k-factor equations require a loading capacitance for delay computation, we use the effective capacitance technique to calculate the effective capacitance for each interconnect wire which is connected to a buffer. Therefore, our delay calculation for buffered interconnects is analytical and thus very efficient. Our experiments show that signal waveforms estimated by our method are very close to SPICE's results.