Channel shortening is often necessary for demodulation of multicarrier signals, complexity reduction of maximum likelihood sequence estimation (MLSE), and can be used to suppress interference in multiuser detection. The Maximum Shortening SNR (MSSNR) and Minimum Mean Squared Error (MMSE) designs for channel shortening are popular in the literature due to their ease of implementation and near-optimality. This paper proposes a method to reduce the complexity of computing the matrices in the MSSNR design by a factor of 140 (for typical ADSL parameters) relative to the methods of Wu, Arslan, and Evans, for a total reduction of a factor of 4000 relative to the brute force approach, without degrading performance. A similar technique is presented for the MMSE design, reducing the matrix computation by a factor of 16 (for typical ADSL parameters).