This paper tries showing which are the factors that serve as a foundation for calculating or projecting the yield of the investor, only considering the effect of financial leverage, without resorting to the application of the more basic tool than it is the Internal Rate of Return (TIR) like traditional methodology of work. Before displaying this formula – main contribution of the writing -, it is described of what the term “financial leverage” consists and how its application results in a direct and quantificable benefit for the investor. An analysis with the more basic mode of payment of the financial liabilities is considered: interests and capital at the end of the term, corresponding to one first approach for finding a series of equations nonlinear that allow to project the TIR of the investor according to n variables. It is assumed that the taxes do not exist, nor effect of the tributary benefit, as well as the costs of bankruptcy and those of agency.