A theory has been developed to calculate fixed polarity Reed-Muller spectra over GF(5) from disjoint cubes representation of 5-valued functions. The algorithm makes use of the properties of disjoint cubes and allows the determination of the spectral coefficients in an independent way. It is simple and can be implemented with small amount of storage space. The algorithm is interactive so the users can manually determine the generation of a part of a spectrum. At the end of the article, experimental results of the algorithm for several 5-valued test files are shown.