This paper proposes a new fast method for calculating modular multiplication. The calculation is performed using a new representation of residue classes modulo M that enables the splitting of the multiplier into two parts. These two parts are then processed separately, in parallel, potentially doubling the calculation speed. The upper part and the lower part of the multiplier are processed using the interleaved modular multiplication algorithm and the Montgomery algorithm respectively. Conversions back and forth between the original integer set and the new residue system can be performed at speeds up to twice that of the Montgomery method without the need for precomputed constants. This new method is suitable for both hardware implementation; and software implementation in a multiprocessor environment. Although this paper is focusing on the application of the new method in the integer field, the technique used to speed up the calculation can also easily be adapted for operation in the binary extended field GF(2m).