Currently the hottest two domestic macroeconomic issues in the United States are the dynamics of the federal funds rate (FFR) and the deterioration of income inequality. Amid the great uncertainty over the FFR, this paper attempts to predict where the FFR is bound to go in the near and foreseeable future with income inequality as a central determinant in the analysis. Interest rate and income inequality are traditionally studied in isolation from each other by two different groups of economists. Nevertheless, this paper hypothesizes a causal relationship between income inequality and interest rate and the hypothesis is verified by the US and Japanese data. Upon the hypothesis and its empirical evidence, the paper tentatively predicts that the Federal Reserve would have to reverse its QT operation and the FFR would be bound to go down again and slip towards zero, if income inequality in the US is not to reduce.