The key assumption of the Tool is that the cash flow (pre-tax and after-tax) of any investment and not past performance equals almost always the future return of the asset at duration.  The following charts compare the starting yield black line (return forecast) with the subsequent future return blue line.  If the lines are on top of each other, it means that the starting yield level is indicative of future returns.  Additionally, the red line is the historical return, and it does not relate to the future return blue line. The data is rolling monthly. The fixed income data started on January 30, 1976, and the stocks data started on January 31, 1950.